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Troubleshooting 4 and 5-Way Wiring Installations

Wiring issues can be frustrating and time consuming to fix, especially when you are not sure where to begin troubleshooting. When your trailer lights aren't working, your trailer is not working, and you are losing valuable time and money. Using the following information and testing procedures, you should be able to locate and eliminate the most common issues encountered during or following a 4 or 5-Way wiring harness installation and get back on the road as soon as possible.

Where to Begin

When it comes to troubleshooting a wiring installation, testing is everything. A lighting problem can originate at any point along the wiring on either the tow vehicle or the trailer, so it is important to determine not only what is causing the problem, but where it is located. The question the troubleshooter will find themselves asking is "There are so many things to check. Where do I start?"
Vehicle Wiring System versus Trailer Wiring System Image
Perhaps the most helpful thing you can do to start troubleshooting is to determine whether the problem is on the tow vehicle or on the trailer. When you use your trailer to test, you have no way to know for certain whether the problem stems from an issue with the wiring harness because the trailer's wiring system is still part of the equation. Testing the vehicle without the trailer will allow you to separate the wiring system into manageable sections.Use the testing procedure described in Method 1 to check for function at the vehicle's 4-Way plug. If all the functions come out correctly at the vehicle plug, you will know that the problem only appears when the trailer's wiring system is connected and you can concentrate your efforts on the trailer.

What Tools Do I Need?

The most helpful tool to use will be a 12V probe-style circuit tester. Click here to see our circuit testers. In addition, you will want to have basic wiring tools on hand. These include electrical tape for repairing connections, a wire stripper for cleaning up wire ends, dielectric grease, and various wiring fasteners like butt connectors, quick splice connectors, or ring terminals, depending on the type of repairs required. Wiring kits that include these items are available.A trim fastener removal tool can reduce the time needed to access your tail light wiring, particularly in SUV and minivan applications, but a flat-head (slotted) screwdriver will often work just as well. A power drill will be used to install the screws for the ground wires. A 12V battery can also be useful for testing trailer lights in situations where you don't have access to the vehicle or you suspect an issue with a particular trailer light.
Troubleshooting Wiring Tool Checklist Image

Common Wiring Issues

ProblemPossible IssuesTesting Procedures
Trailer lights work except for one function: brake, right turn, left turn, or tail.
  • Harness wires are not connected to vehicle correctly/securely.
  • (Plug-In Only) A set of connectors is not seated together properly or is not making a good connection.
  • (Plug-In Only) A required fuse or relay is blown or missing.
  • (Hard Wire Only) Vehicle has separate turn signal and brake lights, brake wire is not connected.
  • Insufficient ground or short to ground on trailer or vehicle side.
  • Method 1
  • Method 2
  • Method 3
  • Method 4
None of the trailer lights work for any functions.
  • (Powered Converter Only) 12V power wire is not connected to vehicle battery.
  • (Plug-In Only) Harness is made for models with a factory tow package, vehicle does not have tow package installed.
  • (Plug-In Only) A required fuse or relay is blown or missing.
  • Harness does not have a connection to ground.
  • Harness has been overloaded.
  • Connect 12V power wire directly to vehicle battery.
  • Use correct plug-in harness for vehicles without a factory tow package, if available.
  • Method 1
  • Method 2
  • Method 3
  • Method 5
Trailer lights worked when the harness was first installed, but eventually stopped working on one or all functions.
  • Ground location for harness or trailer connector is weak or ground connection has loosened over time.
  • Harness has been overloaded due to excessive draw from lights or a short in the trailer wiring.
  • Method 1
  • Method 3
  • Method 4
  • Method 5
Using one turn signal engages the turn signals on both sides of the trailer.
  • (Hard Wire Only) Vehicle has combined brake and turn signals, brake light wire on harness is not grounded.
  • Insufficient ground or short to ground on trailer or vehicle side.
  • Method 1
  • Method 2
  • Method 3
  • Method 4
Turning on head lights in the vehicle causes one or more of the trailer lights to stop working.
  • Insufficient ground or short to ground on trailer or vehicle side.
  • Harness is overloaded when tail lights are engaged because the trailer has too many running lights.
  • Method 1
  • Method 3
  • Method 4
  • Method 5
One or more functions stays turned on, even when the vehicle ignition is off.
  • (Hard Wire Only) Incorrect connection to vehicle wire.
  • Insufficient ground or short to ground on trailer or vehicle side.
  • Harness has been overloaded.
  • (Powered Converter Only) Trailer has LED lights which can be powered by the low-level residual voltage present at the 4-Way plug.
  • Method 1
  • Method 2
  • Method 3
  • Method 4
  • Method 5
  • LED lights may remain on dimly whenever trailer is connected to vehicle. Disconnect trailer when parked for extended periods.
Harness functions correctly at the vehicle side 4-Way plug until trailer is connected.
  • Insufficient ground or short to ground on trailer.
  • Harness is being overloaded when trailer is plugged into vehicle.
  • Method 3
  • Method 4
  • Method 5
(5-Way Only) Trailer reverse lights or reverse lockout function are not functioning.
  • Fifth wire from harness is not attached to reverse light circuit on towing vehicle.
  • Insufficient ground or short to ground on trailer.
  • Attach fifth harness wire to vehicle reverse light circuit.
  • Method 2
  • Method 3
  • Method 4

Basic Testing Procedures

Method 1: Testing for Function

At the 4-Way Plug
  • Use a 12V probe-style circuit tester to check for function at the 4-Way plug. Click here to see our circuit testers. (Figure 1). Have a helper sit in the front of the vehicle to engage the functions while you test.
    • (Powered Converter Only) Before testing the harness for function, remove the fuse on the power wire for 30 minutes, then reinstall it. This fuse should be located close to the vehicle battery, contained in a fuse holder. If the powered converter box has engaged its circuit protection feature, this will reset the box unless it was overloaded to the point where the internal connections were damaged.
    • Do not plug a trailer into the 4-Way plug until function has been verified with a circuit tester.
  • If any function does not have a correct power reading at the 4-Way plug, test the wiring going into the converter box from the vehicle side.
  • If functions are correct at the 4-Way plug, proceed to testing on the trailer.
Testing Function of 4-Way Plug Image
Behind the Converter Box
  • Test to ensure that the signals are going into the converter box from the vehicle side (Figure 2).
    • 2-Wire vehicle: Green (passenger side) and yellow (driver's side) wires should carry turn signal and brake light functions.
    • 3-Wire vehicle: Red wire should carry brake light function, turn signals should be on green and yellow wires.
  • If any function does not have a correct power reading, look for:
    • Plug-in harness:
      • Connectors that are not securely seated together or were not plugged in flush.
      • Loose wires behind connectors.
      • Missing tow package/trailer wiring fuse(s) or relay(s).
    • Hardwired harness:
      • Loose ground connection or weak ground connection.
      • Wires not connected to the correct wires on the vehicle.
Testing Function of 4-Way Plug Behind the Converter Box Image

Method 2: Verifying Correct Wire Connections

Hardwire Installation
  • Make sure that each wire is connected in the correct location (Figure 3). Standard wire colors are listed, but check connections by function if colors vary.
    • Brake wire must be grounded with white wire if vehicle has combined turn signals and brake lights
    • (Powered Converter Only) 12V Power wire should be connected directly to the vehicle's positive battery terminal with the included fuse installed in line. This wire is required for the harness to function.
    • (5-Way Only) If trailer requires a connection for back-up lights or a reverse lockout feature, ensure that the fifth harness wire (typically blue) is connected directly to the vehicle's reverse light circuit.
How to Verify Correct Wire Connections Diagram

Trailer Wiring Color Code

ConnectorFunctionHarness Wire ColorWhere to Attach - Vehicle SideWhere to Attach - Trailer Side
4-Way and 5-WayRight TurnGreenVehicle's right turn signalTrailer's right turn signal
4-Way and 5-WayLeft TurnYellowVehicle's left turn signalTrailer's left turn signal
4-Way and 5-WayGroundWhiteVehicle ground point - metal, uncoated, rustproofTrailer ground point - metal, uncoated, rustproof
4-Way and 5-WayTail/MarkerBrownVehicle's tail light circuitTrailer's tail lights
Only 5-WayReverseBlueVehicle's reverse light circuitTrailer's reverse lights or electric lockout solenoid
This chart is a typical guide; wire colors may vary based on manufacturers. Use a circuit tester to verify connections.
Plug-In Installation
  • (Powered Converter Only) Make sure the 12V power wire is connected to the vehicle battery and that the inline fuse is not blown.
  • If the harness is intended for vehicles with a factory tow package, verify that vehicle is equipped with tow package and that all required fuses/relays are installed.
    • Contact dealer with VIN to verify vehicle equipment.
  • Confirm that the part number on the harness is correct for the year, make, and model of the vehicle.
  • Ensure that harness connectors are installed on the correct sides of the vehicle.
    • Green wiring goes to the passenger side.
    • Yellow wiring goes to the driver's side.
  • Make sure connectors are seated together properly (Figure 4).
    • Disconnect the harness from the vehicle and reconnect it, ensuring connectors click together.
  • Inspect vehicle and harness connectors for:
    • Bent or loose pins.
    • Loose or damaged wires.
    • Broken locking tabs.
Verify Correct Wire Connection for Plug-In Installation Diagram

Method 3: Checking Ground Connections

On the Towing Vehicle
  • Check the ground area for any paint, corrosion, or buildup.
    • If any is present, thoroughly clean the area until bare metal is visible.
  • If using a factory ground screw, verify that no other ring terminals are stacked below the ground for the wiring harness.
    • If present, move ground for harness to a new location or move it to the bottom of the stack (Figure 5).
  • If ground area is already clean, disconnect the ground wire and attach it to a long piece of wire. Run this wire to the vehicle's negative battery terminal for testing purposes.
    • If this solves the issue, the ground wire can be permanently run to the negative battery terminal or moved to a new location with a verified connection to ground.
Checking Ground Connections on Towing Vehicle Image
On the Trailer
  • Make sure that the ground wire (usually white) on the trailer connector is securely attached to the trailer frame.
    • If the trailer tongue folds, place the ground connection on the main body of the trailer frame, behind the tongue hinge.
  • Check the ground area for any paint, corrosion, or buildup.
    • If any is present, thoroughly clean the area until bare metal is visible.
  • Move the ground wire to the trailer frame if it is attached to an aluminum section of the trailer body.
  • Each component should have its own ground for the best performance (Figure 6). This reduces the risk of a ground issue on one component impacting the whole wiring system.
Checking Ground Connections on Trailer Image

Method 4: Finding Other Possible Issues

  • Inspect the wiring for any damaged areas where copper is visible or any spots where the jacketing on the wire is broken.
    • Repair or replace any damaged wire sections (Figure 7).
    • Pay close attention to areas where wire might run near moving parts.
    • Inspect and replace any butt connectors, splice connectors or direct splices that may have worked loose or are not making a secure connection.
  • Check the trailer and vehicle plugs for corrosion.
    • Corrosion will usually be green or white in color.
    • If present, replace the plug or clean it thoroughly with battery terminal cleaner and a wire brush.
  • If the trailer lights ground through the mounting hardware, make sure that the light mounting area is clean and paint-free, and that the surface is not made of aluminum.
    • If the mounting surface is made of aluminum, connect a wire to the light stud and ground it to the trailer frame.
  • Verify that the bulb in each light is functioning correctly.
    • If damaged, replace the bulb or light assembly as needed.
Looking for Other Wiring Issues Image

Method 5: Checking for an Overload Situation

  • Check harness instructions for maximum amperage rating. Determine amperage draw of trailer lights and confirm that lights do not draw more power than the harness can handle. View the table below for amperage draws for some of the most commonly used trailer lights.
  • (Powered Converter Only) If the trailer lights are overloading the harness, it is possible that the unit can be reset if the overload is not extensive.
    • Remove the fuse from the power line and leave it out for 30 minutes before reinstalling it. Then, use a circuit tester to check for function at the 4-Way plug.
    • Do not plug in the trailer before testing the vehicle's 4-Way plug.
  • If all functions are present after resetting the unit, this indicates that the trailer may have a short that is causing an overdraw on the system, or that the trailer lights draw more amperage than the harness is rated to handle.
    • Try removing bulbs from additional clearance lights and connecting the trailer to the vehicle. If the harness continues to work correctly with the bulbs removed, this points to an overdraw from the amount of lights on the trailer.
    • Remove some clearance lights if possible or replace lights with the LED versions which draw much less power.

Amperage Draws for Common Trailer Lights

Incandescent Light

Tail Light Circuit

Stop/Turn Circuit

LED Light

Tail Light Circuit

Stop/Turn Circuit

ST70RB
ST70RB Part Image
.5 amps2.4 amps STL70RB
STL70RB Part Image
.054 amps.362 amps
ST9RB
ST9RB Part Image
1 amps2.5 amps STL9RB
STL9RB Part Image
.062 amps.259 amps
ST17RB
ST17RB Part Image
.9 amps2.3 amps STL17RB
STL17RB Part Image
.121 amps.279 amps
MC44RB
MC44RB Part Image
.2 ampsN/A MCL44RB
MCL44RB Part Image
.054 ampsN/A
MC44AB
MC44AB Part Image
.2 ampsN/A MCL44AB
MCL44AB Part Image
.054 ampsN/A

For more information, see:

Trailer Wiring DiagramsRouting the Power Wire for a Trailer Wiring HarnessUpdated By: Dani S.Last Updated: 3/2/2021

Questions and Comments about this Article


Tom M.
2021 F350 super duty with tow package, No problem with 5th wheel but this weekend was trying to tow 6X12 with new 2 1/2 inch with new 2” ball. Repaired several wires leading to 4 pin on trailer with ne butt connectors. Got intermittent fault on my trailer status for Right side brake and turn signal, returned to starting point redid but connectors on several wires , same result. After 3rd tried elected not to tow trailer. Other trucks were hooked up with no problem, trailer was towed led by a F-150 “without’ problem but don’t know if they had the trailer status sensor that I have. Being told it was because I had a ne hitch and just drive with it and the problem will cure itself, and thoughts
Etrailer Expert
Reply from David B.

Have you tired hooking up to a different trailer to see if the same issue happens? It feels like this may be the truck and not the trailer since other trucks had no issues with the trailer. Test your vehicle end connections and see if you can find any loose wires/ground or shorts.

Reply from Tom M.

@DavidB No problem with my 5th wheel. Test light on bumper 4 pin outlet all work with test light. Don’t get ground off ball but would that cause intermittent fault on only 1 leg of the trailer?

Etrailer Expert
Reply from David B.

Ok, it's in the trailer wiring then. Something somewhere got crossed, also triple check those grounds to make sure they are good too. It's a fault in the wires somewhere.

Etrailer Expert
Reply from David B.

Ok, it's in the trailer wiring then. Something somewhere got crossed, also triple check those grounds to make sure they are good too. It's a fault in the wires somewhere.

Roadking163
I have a 06 f150 that has a factory 7way and 4 way always has worked fine then all the sudden the tail lights and blinkers on both sides quit At same time turn on headlights and nothing in the rear works at all brk lights are very dim if headlights are off but nothing works in rear while the lights are on when I hook up the trailer with the 4pin the tail lights work on the trailer and the left blinker makes the right blinker blink on the trailer still nothing on the truck any clues I’m guessing bad grounds somwhere just seems odd to me thank you any help is appreciated
Etrailer Expert
Reply from David B.

Yeah there is a bad ground or something is damaged along the wire harness. It wouldn't hurt to check all of your fuses too.

Will H.
I haven't towed anything for a while with my 2016 Town and Country but just bought a small used 4 x 4 trailer with minimal lights. Town and Country -4 pin connector had a lot of corrosion. Even after cleaning had no lights for 4 pin tester -Cut off 4 pin connector from vehicle and spliced in new 4 pin. (copper wiring on white ground wire was black when stripped) - at this point 4 pin tester still showed no connection. - added new ground wire to frame to connect to 4 pin connecter. 4 pin tester now shows each wire works Trailer -bought it wire bare wires at hitch. Prior owner had it wired to 5 pin connector to match his vehicles connector -added 4 pin connecter -no lights when attached to van -checked ground on trailer and verified all wire connection -still not even a hint of lights -took alligator clips to small 12 battery attached negative to ground and positive one at a time to the other pins. -with simple 12 battery each light section lights up when the corresponding pin is connected Leads me to believe problem is with van.....but not sure what to test next
Etrailer Expert
Reply from David B.

Make sure you check all the vans fuses and ground points too then check the wire harness for kinks, breaks and shorts. It might be easier and faster to just replace the wire harness since it has a chance of being damaged. I have a plug-n-play harness that is super easy to install # 118534 .

Janzen P.
Installed a new 4 pin connector on the trailer side. Has led test lights that tell me juice is coming from my Nissan Frontier. Everything is working as it should except my license plate light. Do I need to ground the actual bulb inside of the lens?
Etrailer Expert
Reply from David B.

Def check the ground and also make sure the wire itself is not damaged or shorted out.

Mark G.
I bought a "Tow Ready" Draw Tite 7-way 5th wheel Tow Harness Extension for my 2021 Silverado 2500HD. The trailer is brand new 2022 Grand Design Reflection. I have everything from my truck to trailer working perfect. When I installed the new extension, I get no power thru the new harness. Dont understand why.
Etrailer Expert
Reply from David B.

I'd be money the harness is wired different or something got crossed. I wouldn't use the color codes, the safest bet is to get a circuit tester and test each connection while hooked up and see what ones are going through and what ones are not. Then you can use the wiring guide linked below to get the right connections.

Reply from Mark G.

@DavidB I finally have it working, It looks like one of the contacts in the harness got pushed back & wasn't making contact. Good news is it's working now.

Etrailer Expert
Reply from David B.

That's as easy as it gets! Good to hear it wasn't anything crazy.

Ronnie
My truck 4 way works fine on my three trailers. On the fourth trailer when I plug in the brand new kit nothing works. I have made sure of ground on trailer. Also with test light all four terminals are hot when plugged up. But when checking truck side only just the running light terminal is hot. Very confused on this one. I’ve wired 30 or more trailers ?
Etrailer Expert
Reply from David B.

You shouldn't have power at all four wires at the same time. At most you would have power at 3 wires, never the ground. Something is shorted out or wired to the wrong wire. The trailers color code is probably different than other trailers and you will need to test each circuit to verify. I'll add the link to our Trailer wiring diagrams to help guide you. If you have anymore questions I'll be here to help you our Ronnie.

Jim P.
Added a Tekonsha Trailer Tow Harness Wiring Package (7-Way) 118272 to 2018 Ford Explorer. Towing a bass boat trailer with 5 wire flat plug and using a 5 wire to 7 wire connector to the vehicle harness. All lights work however, when attempting to back the trailer the surge brakes engage and lock the trailer wheels. Double checked the wire installation to the 7 wire plug and it is correct per instructions. I noticed the 5 to 7 wire connector only has 5 poles on the 7 wire side and does not contain a pole for the blue wire pole. Have checked around and cannot find a 5 to 7 wire connector that has all 7 poles. Any suggestions on how to get surge brakes to not lock up when backing with this setup?
Etrailer Expert
Reply from David B.

The blue wire on the vehicle end needs to be wired to the vehicles reverse light circuit. I suggest making sure that this is done and using a circuit tester verify the vehicle end connector is getting power while in reverse. Next make sure that the pin for the blue wire is the same pin on the adapter you are trying to use. If not you'll need to rewire the connector to make the blue wires line up. Again once that is done test the circuit while connected to make sure power is going through the connectors. If this still isn't working check your solenoid to see if it is working proper. Make sure all your ground connections and fuse/circuit breakers are in good working order too. I linked some help articles for 5 pin wiring to help too. Let me know if you need any more troubleshooting.

Cody K.
I'm having an issue with my brand new trailer not having any tail lights or running lights and when I turn either the right or the left blinker on, both tail lights start blinking but the clearance light don't blink even though they are wired up with the tail lights. All the lights worked properly on another trailer and worked for a moment on this trailer but now the ONLY thing that works is the brake lights but they still don't work as running tail lights, only light up when I hit the brake pedal then go dark
Etrailer Expert
Reply from David B.

Let me see here, *flips through random book* yeah its a bad ground(not uncommon) or it was damaged(again not uncommon). Get a circuit tester and check the connectors and work your way back to the lights. Check all your grounding points and make sure the trailer connector is clean inside. I'll add some links to wiring diagrams and in-depth troubleshooting to help you out.

Rey
Hi, I have been having with my trailer converter, I have a Hopkins 46255, the problem is the tail light (on the trailer) remain ON even when everything is OFF on the truck, I already replaced for another converter brand new but the next day back to the same problem, I don't know what it is happening
Etrailer Expert
Reply from Les D.

@Rey it seems like a failure of the converter box. My guess is that some wiring on the trailer has grounded out somewhere causing the converter box to burn up. While disconnected from the truck, I would test each trailer wire for shorts to ground. Then, while the truck is still detached I would also check the wires on the trailer connector for proper voltages.

Reply from Rey

@LesD thank you so much for your response, I'll check ??

Jerry B.
I have replaced the 4 pin plug and wiring on my boat trailer. The side lights are working, but nothing with my rear stop/brake lights. Wires ohm good and put new lights on. Ground seems fine. Even ran wire from negative battery terminal to ground wire. Checked fuse that supplies power to relay for trailer stop/turn. Any help would greatly be appreciated.
Etrailer Expert
Reply from Les D.

@JerryB this should not be too much trouble to sort out, but it requires being methodical in your elimination of issues. I have attached an article out lining the method. First let's see if when the trailer is detached, that you have signals on your vehicle working ok. Then test all functions on the connector on the back of your vehicle. You might even connect your vehicle to a different trailer. Bottom line is that we need to first determine if the issue is with the vehicle or the trailer. Next is grounding. There is a white ground wire off the back of the connector that screws to the vehicle. Remove it. File connector till shiny, and do the same for where it is screwed to the vehicle. Do the same for the white wire on back of the trailer connector. By the way, check for loose wires on both connectors. If you ran a wire from the battery ground to the trailer that should prove out your grounds to that point. Tell me about the four pin connector on the vehicle. Was it factory installed or spliced in? Look at where the wires come out of the back of it. Do they connect to a factory harness or connect to the wires from the tail light. There could be a not-enough power issue.

Barry H.
Factory tow package on 2007 Ford Explorer Eddie Bauer. Hooked up trailer - 4 pin flat connectors and turn signals work fine but I get no tail or brake lights. Probed the vehicle connector and yellow / green blink just fine. Nothing from brown. The connector runs to a dual plug connection on the passenger side of the truck. Under dash fuses were checked and seem OK. I checked anything that had "Trailer" in the description. What else to do? Buy a new 4 pin connector to the factory pugs under the truck?
Etrailer Expert
Reply from Les D.

First, let's assure that we have an excellent grounding system. behind the 4-pin connector on your explorer you will find the white wire attached to the metal frame. Remove that and file the frame location to clean bare metal. Also file or sand the ring terminal at the end of white wire. Same where the white ground wire is attached to the trailer up at the front. It would be really handy if you could connect to another trailer and see if you have the same problems. if not, disconnect the trailer wiring and check the voltage in the connector when each lighting function is used. While we are there let's make sure the 4-pin connectors are not rusted. If they are rusted, then replace them. It will be only a matter of time before you have new issues. You may find Item # I26 helpful to make quick checks of the vehicle side plug. If you have no power on the brown wire you will need to trace to the source. I would double check your fuse to that wire as well.

Ron B.
3year old ForestRiver surveyor trailer. Running lights and all turn and brake were working. While on the road we noticed the running lights only stopped working on rear and rear side marker lights. They appeared to be out but on closer inspection the right rear tail light and side marker light were glowing dimly when powered by a separate 12volt source. The fuse in towing vehicle had blown that supplied the trailer lights. Front side marker and front lights illuminate fine on separate when tested. Brake and turn still operate ok on tow vehicle power too. We assume we are looking for a short in the wire that runs only the running lights on the back half of the trailer that might be drawing more current than the fuse can handle. Wondering if the dim glowing lamps on right rear corner says anything to an experienced trouble shooter as to where to continue looking?
Etrailer Expert
Reply from Les D.

First, let's determine if the problem is on the vehicle side or the trailer side. Using a circuit tester like # PTW2993 . test the four wires at at the 4-pin connector on the back of the vehicle. I like the incandescent testers as they draw more power to illuminate the bulb indicator light. If you do not have proper power then start looking on the vehicle side. First check the white ground wire off the back of the connector. It should be screwed to a metal part of the car nearby. File and connection point to bare metal and sand the connector ring at the end of the wire. If it is one of the other wires you will have to trace the circuit back to power, and check fuses. If the problem is isolated to the trailer, once again check the grounding at the trailer. Check the power at each light, and check grounding at each light. Otherwise follow the troubleshooting guide you commented at.

Reply from Ron

@LesD We found the issue some time ago doing exactly what was suggested. Starting at right rear side marker light and working across the rear to left side marker. We brought each of those on till we had all the lower lights working. When we connected the wire that forest River ran up inside the wall to the top markers and camera power the short appeared again. I disconnected the ground and power feed and ran a separate pair out side to test. Builder must have pinched it or crushed it some how causing it to fail. Everything works now but we had to run a new wire set up to top to do it. No way to get it inside the wall so ran som molding in exterior of unit to protect wires. Should have been a conduit in wall between upper and lower lights. Thanks for the reply Ron

Etrailer Expert
Reply from Les D.

@RonB Excellent troubleshooting work!

Ben W.
Installed plug and play harness on my truck. Now the green wire is constantly hot on the 4 pin plug. Makes the passenger tail light stay lit like brake is on all the time. Anyone else ran into this? Have a remedy?
Etrailer Expert
Reply from Victoria B.

What year, make, and model truck do you have? Is the plug and play harness you installed one that has a powered converter box for the trailer lights? If so, test the green wire going into the box and see if it has constant power. It should not - it should only show power when your brake pedal is pressed or the right turn signal is on. If it is showing constant power then there is something going on with the truck's wiring. If it showing power correctly, but the green wire coming out of the converter box has constant power then that is an indication there is a short inside that converter box and it would need to be replaced.

John D.
2014 Toyota Camry hybrid. All turn signal lights work. Only thing that not comes on are brake or stop lights at night
Etrailer Expert
Reply from Victoria B.

Have you been able to determine if the issue is on the vehicle wiring harness or if the issue is happening somewhere on the trailer wiring?

Jonathan
2016 Ford Explorer, plug in connector....worked fine when I installed, now no power to the flat connector. Checked connection - good. Wires from vehicle go from connector inside body - can't really trace them. Not sure where to look next??
Etrailer Expert
Reply from Victoria B.

I would check your trailer wiring fuse(s) on your Explorer to see if they have blown and need replaced. From what I could find in the online 2016 Explorer owner's manual, fuse location 70 takes care of the trailer tow stop and indicator signals.

Bill C.
Hi, I've got a 4 way flat connecting to a trailer. I have all functions except brake lights on the trailer. I am puzzled because the brown wire is for brakes and tail lights. I have traced it to the vehicle. The vehicle has brake lights and tail lights combined. LED lights. I've checked the ground so far. Thanks
Etrailer Expert
Reply from Victoria B.

On a traditional 4-Way trailer connector the functions by wire color are: green - right turn and brake, yellow - left turn and brake, brown - tail light, white - ground. I don't think I've ever run into a brake signal and tail light signal carried on the same wire. If you're sure the issue is on the vehicle side and since you said you've already checked the ground, I would check the trailer wiring fuse locations on your tow vehicle, if your vehicle has them. Since only the brake light wiring is not working, it may be that the trailer brake fuse has blown and needs replaced.

Al A.
I have trailer brake/running/turn signal that the turn signal is not working. I tested the lead that goes to the light and the tester blinks so apparently there is power to that lead. I put in a new light and have the same issue. Could this be the result of a weak ground or? All other lights work fine although the other rear turn/running/brake light is pretty dim. Thought on what I should do next? Thx!
Etrailer Expert
Reply from Jon G.

Whenever there is an issue with trailer lights the best 2 things to do are check all of your connections (including grounds) to make sure that they are clean and secure, and to check your wires for any damage.

Reply from Al A.

@JonG Thx Jon. I’ll clean the grounds today and see if that makes a difference. I suppose it could be the light itself but I put a new light in and had the same result. If cleaning the grounds doesn't work I’ll take the starboard side light and swap sides. I know that light works. Seems I’m always fussing with trailer lights.

Etrailer Expert
Reply from Jon G.

@AlA That's a good plan. Just know that troubleshooting lights is a very common question here at etrailer so you aren't alone!

Oak
hello I have a after market dual 7 & 4 pin connector on my car when I check voltage on 7 pin I get 12 v but when I check the 4 pin I get only 4v nothing else and non of my trailer lights work when plugged in I believe this start happening after I accidently dip the dual connector in water while launching a boat, any thoughts or recommendations? (my trailer lights tested good with another vehicle) thanks.
Etrailer Expert
Reply from Jon G.

Check your fuses, connections, and the plugs themselves to make sure everything has a solid and clean connection. I'm guessing your trailer plugs in via the 4-Way? Are you getting the correct functions and voltages when testing the light functions on the 7-Way?

Reply from Oak

@JonG Jon thanks for replying to my question so I resolved the issue my converter burn up after the 4 pin got dipped in water.so after I replace it with a new one all my lights work like new.

Etrailer Expert
Reply from Jon G.

@Oak Awesome! Glad to hear that you were able to get it fixed.

Mike S.
Just purchased a used Trailmaster trailer. Had a DrawTite hitch installed on my 2018 Nissan Pathfinder. Replaced the trailer side 4 pin connector to accommodate the new vehicle side 4 pin connector. I have lights in all markers and lamps, and left turn signals. I have no right turn signals, and no brake lights in either lamp. This would seem to rule out a grounding issue. ALL bulbs are functioning. I've looked at right side wire (brown and green) and I don't see any exposed wire. All splice connectors seem solid. What am I missing???? Thanx in advance!!!
Etrailer Expert
Reply from Jon G.

First rule of thumb when it comes to troubleshooting wiring is that it could almost always be a bad ground so I would never rule that out. What I would start of doing is isolate which side of your towing setup the problem is on. Try testing the pins on your vehicle 4-Way and then test your trailer 4-Way by either applying 12V power to it or hooking it up to another vehicle that you know is working properly. Let me know what you find and we can go from there.

Drobertson
I have a new utility trailer that came with a wiring kit. After inspecting the kit, I find that the end that I would normally expect to have the 4-way connector only has the four colored wires hanging loosely. What is the most logical way to proceed? Do I solder the ends to a connector or is there a type of connector that can be opened and the wires connected inside?
Etrailer Expert
Reply from Jon G.

You can definitely use a connector like the Hopkins # HM48192 that allows you to just place the wires into the connector but I recommend doing something a little more solid by using heat shrink butt connectors # DW05744-5 and a connector like the Easy-Pull Harness # HM48114 .

Allan H.
I have a new 12 volt magnetic tow light kit for my 2015 Camry XLE that is not working on my car; but when connected to my neighbour's new 2020 Toyota truck the lights work fine. I connected my tester to my Camry's trailer plug and the indicators light up. My neighbour seems to think that my car lacks the power required for the lights to work?
Etrailer Expert
Reply from Jon G.

That's what I would say too. Have you been able to get it to work with anything else? It might be a bad ground or damaged wiring that is pulling power from the circuits so you aren't able to get full power back to your magnetic lights.

Kent J.
Have a brand new small utility trailer. When connecting the 4-pin flat connector to the vehicle (2019 F150) the trailer lights all function correctly. When using the 4-pin flat to 7-pin round adapter and then plugging the round adapter into the truck the left side turn/brake lights do not work on the trailer. Both the flat and round connectors on the F150 are factory equipped options and were not add-ons. I have tried multiple new 7-pin round to 4-pin flat adapters, and even tried another brand new trailer, and the same situation occurs. I have also tried the trailers on different vehicles with no change.
Etrailer Expert
Reply from Jon G.

You might have a poor ground on the trailer and then a bad fuse or connector on your truck. Have you tried walking through the troubleshooting steps that we show in this article?

Reply from Kent J.

@JonG I'll double check all the grounds and fuses and report back to you. I just thought it odd with multiple trailers, vehicles, and adapters all doing the same thing.

Monk
Vehicle has 7 way round connector appears to be wired correctly. Bought adapter to 4way and everything works except brake lights. Looking in the adaptor, there is no terminal for the red brake pin on 7 way to travel into 4 way. How is a 4 way trailer supposed to get it’s brake signal through this adapter?
Etrailer Expert
Reply from Jon G.

When you say the 7-Way is missing the brake terminal are you talking about for the brakes themselves or the brake light function? The brake light function is normally on the same circuit as the turn signals. Attached is a link to our helpful article about 7-Way wiring. Please note that you'll want to compare per function and not wire color. You might have a fuse that needs to be replaced in your vehicle. You'll want to consult your owner's manual to see what that may be.

Mike G.
I have a 7 pin connector i hooked it to my trailer and the right side light came on all the time so i tested the green pin and got 12 volts with my vehicle off i have a converter installed and i checked the ground when i removed it the yellow was also hot all the time is it possible the converter is bad is there any way to test it or bypass the green wire the vehicle lights work fine on the trailer everything works accept the right brake and turn signal
Etrailer Expert
Reply from Jon G.

Whenever there is a problem with trailer lighting it typically either boils down to a poor ground connection or some faulty wiring. If you checked your vehicle connector and the stop/turn pins were lit up the whole time then the issue is probably on your vehicle and you need to check the wiring. To test the converter you would want to test the wiring going into and coming out of the converter to see if it is the converter or further down the line.



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