Trailer Lights Left Side Turn Signal and Brake Lights Not Working

Question

Question:

Both lights are on. When I hit the brake on my truck the left side doesnt light up. Right side does. Right turn signal works but left doesnt

asked by: Chris W

0

Expert Reply:

Your brake lights and turn signals for each side are on one circuit. The left side turn signal and brake light is generally the yellow wire going into your trailer connector. The first thing to do is check the fuses on your tow vehicle.

Next, inspect and test the connector at the rear of your tow vehicle with a circuit tester, like # PTW2993. If the problem is there then you need to clean it, if necessary, and if that doesn't fix it the problem is in your vehicle.

If everything checks out at the connector then the problem is with the trailer. You'll want to inspect the trailer's connector and clean it if necessary as well. Then you'll want to follow the wiring down the left side of the trailer looking for any damaged or pinched areas on the wire itself. If you find any you'll need to repair them and retest your lights. You will also want to check the ground wires for each light, making sure they're grounded to a clean, smooth surface.

I've attached a help article that may be useful to you. If you try these steps and still nothing works, let me know and we'll troubleshoot further.

expert reply by: Charles S

0

Bart L.

5/22/2020

the left hand turn signal on my 2018 chevy 2500 duramax will operate as normal but that same signal and brake light on my fifth wheel camper doesn't work. The spade in the pickup socket will light up but not blink. the right side spade will blink. any answers? maybe fuse or ?

Chris R.

5/25/2020

It definitely could be a blown fuse under the hood. Check the fuse in the #14 position inside the main box (the underside of the lid will show you where exact this is). This is the fuse on your Silverado that's connected to the trailer left turn/stop light circuit. Let me know what find and we can keep troubleshooting if needed.

Tony

8/15/2020

I have a 19 Ram 3500. When I plug a fifth wheel trailer into the plug in the bed of the truck the left side doesn’t work at all. When I plug it into the bumper it does @ChrisR

Jon G.

8/27/2020

@Tony If that's the case then check the socket in your truck bed for any dirt or debris and clean that out. The next step would be to test the actual wires to see if they carry those functions. If they do then replace the socket with # PK11893. If you don't get those functions then you're going to need to swap out the whole wiring kit # C56070.

See All (7) Replies to Bart L. ∨

Zayd

6/26/2020

I have a similar problem. I have a 2011 Tundra with factory tow package. I'm getting 12V at the right turn/brake terminal in my 7-pin connector but nothing at my left terminal. I can't locate a fuse specific to the left turn tow circuit (my truck's signals work fine). Any ideas on where to look? I'm hoping it's not a wire break somewhere.

Chris R.

6/30/2020

Check out the fuse located in the #44 position inside the fuse box under the hood. I believe this may be tied to the trailer turn/brake signals. If that fuse is okay then your best bet is honestly to take the truck up to a local Toyota dealer because it will be extremely difficult to troubleshoot factory wiring.

Chris B.

6/30/2020

Having a similar issue. Right side everything works fine, no left turn signal on shorelines trailer. Problem started with my 2017 f150, and now persost with 2019 ram. Boat shop hooked a battery up to trailer and lights worked fine. Hooked the ram up to a different trailer and still no left blinker. Checked fuse under hood. Fuse is fine.

Chris R.

7/6/2020

It's very interesting that the issue occurred with two different trucks (seemingly pointing to the trailer as the issue) but also occurs with the Ram when hooked up to a different trailer (seemingly pointing to the truck as the problem....). Sometimes there's an additional factory relay tied to the trailer turn/stop light circuit. I know you checked the main fuse but look through your owner's manual to see if there's a relay as well - if so, replace it to see if it resolves the issue.

Joshua H.

7/3/2020

My 2011 Silverado 3500 diesel Might have an issue. The trailer Left brake light stays on and the signal won’t work if course. The right side is fine. Trailer is a 2013. Checked all the fuses and nothing is blown. Cleaned all the connections as well.

Chris R.

7/6/2020

Have you tested the 7-Way on your Silverado to try and rule out where the issue is? If not, start there- see if you get constant power on that left brake/turn signal pin. If not, then the issue is somewhere on the trailer side. You'll just want to inspect any wiring on that circuit that you can, looking for an exposed portion that may be touching metal (or a neighboring wire).

Adam

7/6/2020

The left turn and brake light for my trailer lights doesn’t work. I have a Honda Odyssey and I’ve checked the rear fuses and the plug for the wiring harness. There is power back to that point for the left turn signal. Could it be the wiring harness itself that plugs into the vehicle in the rear cargo area that needs to be replaced?

Chris R.

7/10/2020

It could certainly be the harness. Have you tested the actual connector at the bumper? See if you get power there on the left turn/brake pin. If you do, then the issue is actually on the trailer. You'll want to check the main ground wires (both on the trailer and Odyssey) to ensure they're still securely attached to a clean, bare metal surface. Let me know what you find and we'll go from there.

Adam

7/10/2020

@ChrisR thanks! It was the converter in the ody that was faulty. I replaced it and all is working!

Chris R.

7/14/2020

@Adam Fantastic!

Joe J.

7/8/2020

Left turn signal light and brake light on 2014 Silverado works but trailer lights don't. I checked the fuse for the trailer wiring #17 on truck it's fine. Checked the wiring on trailer and connector it's fine. I get no voltage but when I take the bulb out I do,now I have another trailer and same thing.

Chris R.

7/10/2020

We at least know the issue is somewhere on the truck. Since taking the bulb out resolves the problem, I'm thinking there's a weak ground somewhere that's affecting voltage. Make sure the main harness ground is still securely attached.

Joe J.

7/11/2020

@ChrisR Thanks actually it was the fuse, looking at it I could not see a break but testing with an ohm meter it was bad

Paul M.

9/7/2020

When l turn on my right turn signal on my truck my left turn signal comes on on my trailer. What is wrong. Thanks

Jon G.

9/8/2020

Sounds like either your truck or your trailer is miswired. Check out the attached articles on 4-Way and 7-Way connectors to see what functions should be on which pins.

Helpful Links

faq-wiring-4-way.aspx

faq-wiring-7-way.aspx

Ricci G.

9/1/2021

@PaulM Hello, I have a 2009 Ford Expedition XLT with a standard factory tow package. The left, right and of course the brake light on my 7pin connector doesn’t work all of a sudden. I don’t have the owners manual so I would like to ask which of the fuse # should I check in the fusebox under the hood. Thank you!

Victoria B.

9/9/2021

If it is just the stop and turn functions, you will want to check fuse location 45 in the power distribution box under the hood. If the trailer running lights are not working, then you'll also want to check location 28 in the same box. These fuse locations are based off what I could find in the online Ford owner's manual for your Expedition

Michael

5/29/2024

I am having a similar issue (left turn signal not working on a 2003 Komfort Trailer). I have: - tested bulbs - I am sure I am using a good bulb - tester light tested for power at the left signal - no power - tester light tested all connectors on the truck - all work as expected - tested trailer plug by using the male plug tester loaned to me by an RV place. This allows to direct connect the power wire to all the other wires separately - all lights worked EXCEPT the left signal Of note: there has been some intermittent connectivity for the running lights - they have worked when connected to the truck sometimes and sometimes not (currently not). Also connected the loaner tester plug as suggested by the technician and pulled the breakaway switch and all lights came on as they should have. Thereafter the truck running lights also worked with the trailer during that testing cycle but currently are not working?? My gut tells me there is an inline breaker or fuse somewhere OTHER THAN at the battery, (found those and they are good), or in the panel in the trailer (tested all those and they are good). Can anyone point me to some hidden fuse or breaker I am not finding? I am at a loss at this point.

Bryce D.

5/30/2024

@Michael That's very odd Michael and I'm honestly a little confused too. Have you checked your ground connections at all? The only reason that comes to my head is that you mention you have intermittent connectivity, which can sometimes indicate a weak or loose ground. If a breaker was flipped, or a fuse was popped, the lights flat out would not work so there wouldn't be intermittent connectivity.

Michael

5/30/2024

@BryceD thank you. Makes sense. How does one check a ground? It is not a tester light thing is it. Am I just looking for a loose wire somewhere? FYI - the latest: Yesterday I returned the tester plug to the RV place and buddy there gave me another breadcrumb trail. Basically he suggested I pull the breakaway switch and test both the black and brown wire coming out the back (both lit up the tester light) then go back to the 1st rear axle and find those wires and test there. If both have power there, then follow over to the opposite side wheel and test, then the 2nd axle, etc. I did find power at 1 of the two wires at the first wheel but ran out of daylight. I'd like to check for grounds if that is easier and then if I find nothing I intend to pick up where I left off on testing the wiring at the brakes on each wheel. This required jacking up the trailer and is a pain, so hopefully I'll find a bad ground wire somewhere. Thanks again for your feedback Bryce.

Bryce D.

5/30/2024

@Michael So typically the ground wire is the white wire so you'll want to look for that. I'd recommend checking first to see if the ground connection is physically loose or visibly damaged. If it is loose, tighten it and check again to see if the problem continues. If it does, try changing the ground location to a spot that is bare metal and has no rust. If that all looks fine, you're going to need to get a voltmeter and check to see if there is power flowing to your lights. If there is not, then you have a breakage somewhere in your harness and you'll need to locate where the power stops flowing.

See All (4) Replies to Michael ∨

Davis

6/14/2024

Right Side Works Fine Left Side is having issues. - Tail Light doesn’t work when headlights on - Light is Dull when it’s working - Left Blinker makes both right & left blinkers work like the hazards are on the trailer. 4 pin hook up, brand new light & harness set from Home Depot. Truck has 4 pin & 7 way outlet - 2016 Colorado Lt I’ve tried hooking it up both ways with an adapter, checked the ground & relocated that. Fuses look good, all connections look solid. Tried with 2 new harnesses from the boat end & nothing works for the left side. Maybe a brand new fuse even though it looks good? I should probably get a meter & check next.

Bud M.

6/15/2024

@Davis Considering you have replaced the harness multiple times it sounds to me like the issue is on your 2016 Colorado. You can always try connecting your Colorado to a different trailer or connecting your trailer to a different vehicle to verify which is the issue. If on the Colorado I would start by disconnecting the Trailer Connector # HM40975 and testing the wiring on your Colorado. This will help you to determine if the issue is inside the connector or if your wiring on the vehicle is causing the issue.

Davis L.

6/15/2024

@BudM - The truck worked with 2 different trailers today. Stopped at Home Depot & TSC. So, now it leads back to that harness, grounding or how the wiring was done on the left side? Just match the 2 colors. Brown/Brown & Yellow/Yellow. Did the same thing for the right side. Pretty confident it’s correctly done for the left.

Bud M.

6/15/2024

@DavisL While it sounds like a harness issue since the left turn signal activates both the left and right turn signals I know you said you already tried a different harness. You are correct that you simply connect the brown to brown for the running lights and yellow to yellow for the left turn/brake light.

See All (4) Replies to Davis ∨

Blake F.

11/24/2024

I have a 2006 Chevy 2500HD (duramax) and every trailer I hook to I have no left turn signal or brake light, 100% my truck is the culprit but I’m horrible with wiring and don’t know where to even start other than the fuse box. Too many for me to know which one.

Kate F.

11/24/2024

@BlakeF Hello Blake. Definitely your truck if this is happening on multiple trailers. If you look at the your owners manual page 5-125 you will see where the LT TRLR ST/TRN (Left Turn Signal/Stop Trailer) fuse is located, I would start there and see if that fuse has gone bad. Then I would test the 7 way on the back of the truck, using something like the Curt 7-Way to RV Socket LED Circuit Tester # C73NR this will make testing pretty simple, turn the left blinker on and the red light should flash, push down the brakes and the red light should stay on. If if doesn't then you know to test the left turn wire behind the connector by using something like the Hook Probe Circuit Tester # PTW2993. You could just have a bad 7 way connector as they do go bad. If that is the case you can just get Curt T-Connector Vehicle Wiring Harness for Factory Tow Package - 7-Way and 4-Pole Flat Connectors # C55774. If there is NO power on the turn wire then you will have to trace it back because there is a short somewhere. The # PTW2993 is great for testing the wire along the way. Could be a faulty connection behind the Chevys left taillight as well. If you are still having issues after trying these steps, please let me know.

Helpful Links

tv-demo-curt-custom-fit-vehicle-wiring-c55774.aspx

tv-review-curt-7-way-to-rv-socket-led-circuit-tester-c73nr.aspx

tv-review-performance-tool-hook-probe-circuit-tester-ptw2993.aspx

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Answer 1

You will first want to check the fuses on your tow vehicle. Some vehicles could have fuses for operating the turn signals and brake lights of a towing package. You will want to check if they are installed and working properly. The next thing is to…

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Answer 2

Most trailer wiring problems are the result of a bad ground. What I would do is start with the connectors. Maker sure the connectors on both the trailer side and vehicle side are free of dirt and corrosion and that they are properly grounded. Next, I…

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Answer 3

Yes, the Trailer Valet XL Trailer Dolly with Chain Drive - 2-5/16" Hitch Ball - 10,000 lbs #TVXL25 will be able to turn your tandem axle trailer without wheel dollies.

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Answer 4

The most likely cause for the turn signals not to work when the running lights are on with your trailer is a bad or weak ground. It's very possible that a weak ground connection can be just strong enough to allow sufficient current for some…

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Answer 5

We know that the Fulton Fender part #F008583 that you referenced will easily fit on a Shoreland'r trailer that has tandem axles but it is not a direct bolt-on application. Some small modifications will need to be made. Check out the review I…

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Answer 6

Both the Roadmaster and Blue Ox tow bars are great options. But if it was my decision to make I would go with the Blue Ox Avail part #BX7420 as we have found that the Blue Ox tow bars are a little easier to connect and disconnect from. Also this tow…

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Answer 7

The first thing that I would recommend checking are the ground connections for the trailer side connector and the lights. Poor ground connections are the most common culprit of trailer wiring issues. The lights will have either a ground wire or they…

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Answer 8

Hey Mark! The B&W Continuum #BW78FR is great for any setup as long as you're in the 600–1,600 lb tongue weight range of the system. The best part about it is you can set it perfectly for any tongue weight so it won't be over or…

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Answer 9

This sounds like a ground problem on the right side. The turn signal not working makes sense because with the brake lights, there is a constant signal coming through which is enough to make the lights illuminate on both sides like they should. But…

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Answer 10

Aluminum does not provide the best electrical ground to complete a circuit. I recommend finding another nearby, bare metal location that is free of any dirt or debris. If you have an aluminum trailer, the best option will be to ground the lights to…

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Answer 11

It sounds like you may have a loose wiring connection or a corrosion problem on the 7-way pin for the right turn/brake lights. This pin is the one at the 3-o-clock position as you're looking at the vehicle's 7-way; please refer to the linked…

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Answer 12

Not necessarily. If your 2015 Lexus RX 350 came with the tow package then you just need the T-One #118252, but if it doesn't have the tow package then you need the T-One #118255 with the converter. The tow battery fuse slot would only be used if…

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Trailer Lights Left Side Turn Signal and Brake Lights Not Working

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