Trailer Wiring Diagrams

6-Pole Diagram

6-Pole Diagram

Trailer Wiring Connectors

Various connectors are available from four to seven pins that allow for the transfer of power for the lighting as well as auxiliary functions such as an electric trailer brake controller, backup lights, or a 12V power supply for a winch or interior trailer lights. Choose a connector that has the required number of pins for the functions required for your trailer. If the connector is under the vehicle, you will want to use a mounting bracket to attach it to the vehicle. This will help prevent damage that may occur if the connector is left dangling.

Trailer Wiring Color Code
ConnectorFunctionColorSuggested Minimum Wire GaugeWhere To Attach - Vehicle SideWhere To Attach - Trailer Side
4 Way & 5 Way6 Way & 7 Way
7 Way6 Way5 Way4 WayRight TurnGreen1816Right turn of vehicle's wiring harnessTrailer's right turn signal
Left TurnYellow1816Left turn of vehicle's wiring harnessTrailer's left turn signal
GroundWhite1612Vehicle ground point - metal, uncoated, rustproofTrailer ground point - metal, uncoated, rustproof
Tail / MarkerBrown1816Taillight of vehicle's wiring harnessTrailer's taillights
Brake*Blue1812Electric brake control, power for brakesBreak away switch
BatteryRed (or Black)12Fuse block or FUSED battery LeadBreak away kit, interior lights and battery charger.
Back UpPurple16Back up circuit of vehicle's wiring harnessBack up lights (if available) / Hydraulic coupler.

This chart is a typical guide, wire colors may vary based on manufacturers. Use a circuit tester to verify connections.

*NOTE: The fifth connection is sometimes used on 5-ways to power a reverse lockout on trailers with surge brakes. When this is the case, the lockout should be connected to the backup light circuit of the tow vehicle.

4-Way Connectors

4-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake lights) plus one pin is provided for a ground wire. Most standard light duty trailers will use a 4-pole flat connector.

5-Way Connectors

5-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake) and, besides the ground, one pin is available to provide support for another function. Typically the 5-Way Flat is used for trailers with surge brakes or hydraulic brakes. The additional wire is tapped into the backup lights to disengage the hydraulic trailer coupler (actuator) when the vehicle is reversing, thus turning off the trailer's brakes.

6-Way Connectors

6-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake). The ground and two extra pins are available to provide two additional functions, typically for electric brakes and 12 volt "hot" lead. The 6-way round connectors are very common on horse trailers. The 6-way square connectors are more common on campers.

6-Way Vehicle Diagram

Note: In some applications, the black battery power connection and the blue brake controller output connection are reversed.

7-Way Connectors

Aside from the three main lighting functions, additional pins for electric brakes, a 12 volt "hot" lead, and backup lights are available. There are two types of 7-way connectors. One has flat pins, which are often referred to as blades. The other has round pins. The round pin style is very rare. The RV style 7-way with flat pins (or blades) is very common. It is often found on newer trucks and SUVs that come equipped from the factory with a trailer hitch.

7-Way Trailer Diagram

7-Way Trailer Diagram

Note: To ensure that your trailer connector is wired properly, we recommend using a circuit tester to match pins by function. Because wire colors can vary, they are not as reliable for determining functions. And improperly connected wiring can cause damage to electric components.

Mounting Your Trailer Wiring Harness

Often the 4-pole trailer connector will remain in the trunk or cargo area of a car or SUV when not in use. This helps to extend the life of the connector by protecting it from the elements and accidental damage. When it is needed for towing, simply pull the connector out and shut the trunk or rear door. The rubber weather strip that provides a door seal keeps the wire from getting pinched. If the trailer connector needs to be mounted under the vehicle, we offer many different mounting brackets that will help to protect the connector and keep it from dangling beneath the vehicle.

Trailer Wiring Adapters

Trailer Wiring Adapter Fitguide

The T-One connectors and hardwire kits all use a 4-pole trailer connector. This connector is most common among the smaller utility trailers and can easily be adapted to match the larger 5-pole, 6-pole and 7-pole styles. Using an adapter lets you avoid having to splice into the vehicle's wiring system. Adapters will plug into the flat 4-pole connector and have wire leads to provide additional functions such as powering trailer brakes, power lead for utility lights, reverse, or auxiliary power for a winch or tools. If your vehicle or trailer is equipped with something other than a 4-way plug, such as the larger 7-way round plug, you can use our adapter fitguide to find the one that is right for your vehicle and trailer.

Troubleshoot Your Trailer Wiring

Troubleshoot modulite wiring

If you have a Modulite (powered converter), Converter, or T-One connector that is not working properly, you need to use a circuit tester to determine the source of the problem.

Converter Shorting Out

When too many amps are drawn through the converter box, it can be shorted out. The possible causes are:

Weak Ground

Video showing how to wire the ground

If you find some, but not all, lighting functions work properly you may have a ground problem. In this situation a weak ground is just strong enough to provide some lighting functions but not all. When the taillights and brake lights are used at the same time, it creates the maximum amp load of the lights on the trailer. If a ground problem exists, it will show at this point. The places to check grounds are as follows:

NOTE: If you purchased your wiring harness from and none of these fix your problem please feel free to contact us so our product experts, and installers can determine possible remedies or warranty coverage.

How to wire your car or truck to pull a trailer

Trailer Wiring Options

By law trailers are required to have at least running lights, turn signals, and brake lights. To provide the power and a connection for these functions, the tow vehicle's electrical system needs to be tapped into. There are two options available for connecting to your vehicle's electrical system, a plug in style T-One connector or a custom selected hardwire kit.

T-One Connector

The easiest way to make this connection is with the use of a T-One Connector, which comes with OEM style connections that simply plug into your vehicle's existing wiring harness, typically near the rear of the vehicle or by the tail lights. Sometimes the vehicle manufacturer will run the wires to an easily accessible plug underneath the vehicle or behind the paneling in the back cargo area. T-Ones come pre-wired with a 4-way flat trailer connection and can be expanded to 5-way, 6-way, or 7-way trailer connections through the use of a wiring adapter.

Custom Hardwire Kit

Scotch Lock Illustration

If a T-One is not available, a connection can still be easily made by using one of our custom selected hardwiring kits. We offer kits with all the pieces you will need to simply tap into the existing wires on your vehicle. This may sound difficult, but quick splices make installing the wiring harness quick and easy. A quick splice has two grooves in it; one groove is for the vehicle wire, and the other groove is for the wire on hardwire kit. Once both wires are in the grooves, you simply press down on the top of the quick splice. This forces a metal piece into both wires, connecting the circuit and eliminating any need for cutting or splicing. To hardwire the tow vehicle for a trailer connector you need to locate the proper wires. To help in this task you can check the vehicle's owner manual or use a circuit tester. The circuit tester is used to make sure the correct wires on the hardwire kit are connected to the matching wires on the vehicle; it helps determine which wire performs which function. The easiest place to tap into the vehicle's wiring system is behind the tail lights. By turning on the left turn signal, a circuit tester can be used to test the different wires behind the driver's side tail light. When the circuit tester lights up, you know that wire carries the left turn function. A quick splice slid through the yellow wire on the trailer connector and around the just found vehicle wire will clamp down to provide a secure connection.

The three types of Hardwire Kits are:

  1. Standard 4-Pole Wiring Harness - For use with vehicles that have adequate power and standard wiring system, these simply connect into existing wires on the vehicle and have a 4-pole flat connector to attach a trailer.
  2. Converter - For use with vehicles that have separate turn and brake light wires. Some vehicles send only one signal per wire, creating what is called a 3-wire system: one wire for the left turn, one wire for the right turn, and one wire for the brake signal (common on vehicles with amber turn signals). A converter will reduce it to a standard 2-wire system needed for wiring a trailer. There are still additional wires for the running lights and for the ground. Any vehicle with amber turn signals will need a converter. However, there are some vehicles with all-red tail lights that can also require a converter. A wiring harness with a converter has a black box built in it. Five wires go into the box, and only 4 come out. The converter transfers the brake signal on the vehicle into the left and right turn signals for the trailer wiring system.
  3. Modulite or Powered Converter - Used with vehicles that do not provide enough electrical power to handle the additional strain of powering trailer lights, the Modulite or powered system draws power directly from the battery but still connects to the vehicle's wiring system to determine when to power the lights on the trailer. If there are too many lights on the trailer for the vehicle's electrical system to provide adequate power, use a modulite or powered converter. A modulite installs the same way as a standard converter except an extra wire must be run to the battery. Instead of drawing power from the vehicle wiring system, a modulite draws power directly from the vehicle battery. This is safer because the extra amps to power the trailer are no longer going through the expensive electrical components of the vehicle. More vehicles are using thinner gauge wire and require a modulite, regardless of how many lights are on the trailer, simply to protect their wiring system.

Wire Color by Vehicle Manufacturer

Dual Purpose Bulb System
Wire FunctionWire ColorGMCFordChryslerJeepToyotaHondaMazda
Right Turn & Brake LightsGreenGreenOrange w/ Blue StripeBrownBrownGreen w/ Yellow StripeGreen w/ Yellow StripeGreen w/ Yellow Stripe
Left Turn & Brake LightsYellowYellowLt Green Orange StripeDk GreenGrey w/ Black StripeGreen w/ Black StripeGreen w/ Blue StripeBlack Stripe
Tail LightsBrownBrownBrownBlack w/ Yellow Stripe or BlackBlueRed w/ GreenRed w/ Black StripeGreen or Black Stripe
GroundWhiteBlackBlack or GreyBlackBlack & BlackBlack or WhiteBlackBlack
Single Purpose Bulb System
Brake LightsUse ConverterPink or Lt BlueRed w/ Green StripeWhiteBlue w/ Black StripeGreen w/ Red or White StripeGreen w/ White StripeGreen or Green w/ Red Stripe
Backup LightsRedLt GreenBlack w/ PinkVioletBrown---
Electric Trailer BrakesConnect To Blue Wire From Brake Controller

Vehicle manufacturers have intermittently changed wiring colors over the years.

It is recommended that a circuit tester be used on the tow vehicle's wiring harness to verify that the correct wire has been located for the proper function.

Questions and Comments about this Article


Which wires get connected to what at taillight? I have two screws to connect. Brown wire and the light would go together to have power. Turn signal wire would also be on this connection? Searched and searched with no answers. Should of taken a picture before I took it apart.Thanks!

Reply from Chris R.

Can you tell me what model tail light assembly you are installing? If the light is serving as both the tail light for running lights and for turn and brake signals, then the turn/brake signal wire would go to it as well. If you can tell me what model light you have though I should be able to give you a more specific answer. 58781

Justin B.

Hey there,I have a 2014 3500 that I use on a regular basis to pull materials for work. I was curious if you knew the amperage or the voltage that comes out of the trailer plug on the back of the truck?The reason I ask, besides not finding any info anywhere, is that we want to install new lights or a string of lights inside the trailer, and wanted to make sure we didnt short it out.Any info would be greatful!Thanks!J

Reply from Jacob H.

I would recommend replacing all of your lights with LEDs and whatever lights you decide to add make sure they are LEDs also. If the lights look like they are dim or flickering you can add a battery to the trailer for the extra lights inside and run a charge line from the 7 pole plug to the positive side of the battery that way it maintains a charge. 54737

Clif P.

I have a 14,000 pound tandem trailer just put new drums and new electric brakes on new wire harness to battery release and vehicle has power to wheels but has no extensive stopping power what do you think could cause The wheels to stop when we left trailer off of ground but on the ground brakes do not have enough power to stop the wheels

Reply from Jacob H.

It sounds like you need to adjust your brakes. If the breaks are not adjusted properly you have a very weak amount of break pressure being applied to the trailer. We have the tool needed to adjust them and I will provide a link to find it. 54486

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