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Trailer Running Lights Do Not Work but Brake Lights and Turn Signals Do Work  

Updated 09/18/2025 | Published 05/25/2015

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Question:

Blinkers and break lights work but tail/running lights dont. Truck tail lights are working. Is it a fuse or is it wiring?

0

Expert Reply:

It could be a tow package fuse on the vehicle. Use the owners manual to find the locations of fuses/relays related to the tow package wiring to check them and replace as needed.

If the issue is not a fuse or relay then you can test the vehicle side trailer connector using a circuit tester such as # PTW2993. Turn the vehicle headlights on and use the circuit tester to test the pins on the connector at the back. If there is no power on the running light pin then there is a break or loose connection somewhere between the connector and where it terminates at the front of the vehicle that you will need to track down.

If everything checks out on the vehicle then the issue is on the trailer. Make sure the trailer connector is clean and free of corrosion inside and out. The main trailer connector ground and the grounds for all of the lights need to be attached to clean and corrosion free bare metal surfaces.

If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by:
0
Michael H
Scott profile picture

Scott

5/19/2020

Hi there. Having a strange issue with my trailer lights. Brake and turn singles work but not my running lights within the brake, turn and running bulb. All other running lights work around the trailer. What’s weird is I have 12.4 volts going to all pins on the plug and yet the running lights still don’t work? The light itself is a single bulb light so not a blown bulb. Any ideas would be greatly appreciated. Thanks so much.

Chris R. profile picture
Etrailer Expert

Chris R.

5/22/2020

That IS a bit strange. Are these new trailer light assemblies (have they ever worked properly with the running lights)? I would start by checking their grounds - whether they ground through a dedicated wire or through their mounting hardware. Make sure they're securely attached to a clean, bare metal surface. Let me know what you find and we'll keep troubleshooting.
Doug M. profile picture

Doug M.

7/16/2020

@ChrisR thank you for the info Chris, i actually found out that i had a blown fuse, i found that the left side trailer lights have a fuse and the right side trailer lights have their own fuse so when i changed the fuse for the left side the lights worked fine
Chris R. profile picture
Etrailer Expert

Chris R.

7/21/2020

@DougM Awesome!
See All (8) Replies to Scott ∨
Doug M. profile picture

Doug M.

7/11/2020

On my 2018 Ram 1500 crew Ref: my boat trailer All my truck lights work but on the boat trailer only the driver side running light and blinker work, nothing works on passenger side trailer (and the boat and trailer are only one month old)

Chris R. profile picture
Etrailer Expert

Chris R.

7/16/2020

I would definitely start by testing the trailer connector on your Ram 1500. See if you are getting power on the passenger side turn/brake signal pin. If so, then the issue is on the trailer side. Since you mentioned that the driver side running lights work - I suspect the problem is likely on the trailer anyway. Make sure the main harness ground is still securely attached to clean bare metal and do the same for each of the individual trailer light assemblies.
Doug M. profile picture

Doug M.

7/16/2020

@ChrisR
Angie profile picture

Angie

8/2/2020

Hello, I have a 2020 Honda CRV. I had Uhaul install a hitch. The trailer we are pulling worked great until we launched waverunner. Now all lights stay on , even when car is turned off. Blinkers and brake lights on trailer do not work. Uhaul replaced plug in play after first time this happened . First time I launched after repair it did it again. Any suggestions?

Jon G. profile picture
Etrailer Expert

Jon G.

8/11/2020

Did you by chance unplug your trailer electrical prior to backing it into the water?
Philipp profile picture

Philipp

9/6/2020

I have a 2015 Dodge Grand Caravan that I had the dealership i bought it from brand new,install a mopar factory trailer wiring harness on. Left and right signals work and brake lights but No Running Lights. I checked owners manual for fuse location and there are no fuses in there. I think when they installed it, they spliced all the connections. I couldn't find any in-line fuses either

Jon G. profile picture
Etrailer Expert

Jon G.

9/8/2020

If your trailer wiring harness isn't working properly and there aren't any dedicated fuses for it then I'd reach out to the dealer who installed it and have them fix what's wrong. If you're wanting to look into this on your end then you'll want to check out the wire used for the running light circuit and see how it was installed to make sure it's still securely connected.
Rob profile picture

Rob

3/21/2022

@Philipp I have the exact same problem and have a model from the same parent company (2015 Jeep cherokee) and was wondering if you found out it might be a Mopar flaw?
Will D. profile picture

Will D.

9/8/2020

Was rewiring my trailer last night and everything was working perfectly. I was wiring the trailer hot as I had the truck on and trailer connected as I was doing the wiring. On the last light I let the positive touch the trailer and I heard a sizzling noise and ban my running lights stopped working. I checked the truck for any blown fuses and nothing. My blinkers work and brake lights. I checked the trailer connection at the truck and my running lights are not working. Could I have messed up the harness?

Jon G. profile picture
Etrailer Expert

Jon G.

9/8/2020

@WillD If you heard a physical noise coming from your trailer lights/wiring then you very well could have damaged something with the harness. You're going to have to trace the wiring all the way from the connector to your lights and even check that your lights are still good as it could literally be anything on that circuit.
Jon L. profile picture

Jon L.

5/10/2024

@WillD Probably the fuse. I had the same problem on my 2013 F150 and 20 amp Fuse #67 was bad. Swapped it out with the 20amp heated seat fuse and the lights worked.
Kirby P. profile picture

Kirby P.

9/8/2020

I a skeeter trailer, and the turn signals, break lights, back-up lights work, but the running lights stopped working. where should i start first looking for the problem?

Jon G. profile picture
Etrailer Expert

Jon G.

9/8/2020

@KirbyP Sounds like you have the same issue as Joan did with her wiring when she asked the initial question. You're going to want to follow the same steps that Michael highlighted on this answer page.
Smarty P. profile picture

Smarty P.

3/9/2021

Experts? There is only one ground pin regardless of which connector you have. If it was a ground issue, no lights would work,
Jon G. profile picture
Etrailer Expert

Jon G.

3/11/2021

@SmartyP Hate to break it to you but each light has it's own ground most of the time. Sometimes people will run all of their grounds together on 1 wire and connect that to the trailer connector, but a lot of times each light will either ground through the mounting hardware or by using a self-tapping screw and a ring terminal on the ground wire. If you don't believe me just take a few minutes to meander through our trailer lights selection (which I've linked for you) and check out the descriptions.
David A. profile picture

David A.

1/10/2021

Hello I have a trailer where the running lights don’t turn on but they flash when I lock my truck I’ve tested fuses checked the plug connections any ideas?

Jon G. profile picture
Etrailer Expert

Jon G.

1/14/2021

Michael gave a few more tips on testing the vehicle and trailer side of your setup. I'd try using his troubleshooting tips so we can figure out where the problem is at.
Garry R. profile picture

Garry R.

3/21/2021

@JonG I have pretty well the same issue. Turn signals and brake lights work, running lights don’t. But brake lights don’t work with the running lights turned on.
Kef G. profile picture

Kef G.

3/24/2021

@GarryR You'll need to check the wires on the vehicle side and trailer side and look for any pinch points or corrosion. If you find any, replace the wires. Also, be sure to check the ground wires' connection points since any rust or corrosion there will cause some things to not work.
See All (7) Replies to David A. ∨
Yroc profile picture

Yroc

6/25/2024

I have a 2016 Jeep Grand Cherokee. My boat trailer brake lights, turn signals all work fine but have no Day Running Lights. All fuses checked out fine. My previous trailer never had this issue (just sold it 3 days ago) All new wiring, grounds are clear and have great contact with bare metal. Please Help im so frustrated ??

Jameson C. profile picture
Etrailer Expert

Jameson C.

6/25/2024

@Yroc I would use a circuit tester like part # PTW2993 to test the wiring of the running light circuit working your way back to the taillight assemblies to find where the voltage stops as that's why the lights aren't working. If voltage is making it into the assemblies though and they still aren't working it's the way the lights are grounded so you'd need to trace the ground wiring back to find the issue. If the assemblies only have one wire that runs to them they ground through the mounting hardware.
Yroc profile picture

Yroc

6/25/2024

@JamesonC ok i will give that a go. Appreciate the quick reply. Will update as soon as i can
Jameson C. profile picture
Etrailer Expert

Jameson C.

6/25/2024

@Yroc Sounds good!
Kevin S. profile picture

Kevin S.

9/5/2024

I am having issues with my running lights on the truck/trailer. I thought I originally had an issue with the relay switch. I had the switch checked and it was determined that was not the issue. What we did to get running lights back to the trailer was to take out the relay and put in a jumper. By doing this I am able to have running lights, but I have power continually to the trailer lights. I was wondering if it could be an issue with wiring harness junction block. I have a 2016 Chevy Colorado LT 4WD 3.6L motor. Any help will be appreciated. Thank you.

Jameson C. profile picture
Etrailer Expert

Jameson C.

9/5/2024

@KevinS Is it factory trailer wiring or do you have an aftermarket harness installed.
Wes profile picture

Wes

9/18/2024

All of my trailer lights work as normal. Besides the running lights on the right side tail light. The brakes and signal works on it. It is not the light itself and I have cleaned the grounds. There are green and brown wires running back and brown wire that runs from the connection to the rear middle bar. At one point i was able to get a faint light while the brake and signal were not on.

Tom B. profile picture

Tom B.

9/21/2024

so, I have the same issue.. however, on my vehicle side my 4 pin flat has indicators to let me know they're getting power. I have brakes, turn signals, but no running lights. I used a wire wheel on my drill to prep the ground spots for each light and the ground to the trailer. the indictor on my vehicle side says I am getting power there. it almost has to be the ground? right? or corrosion on the vehicle side plug - (trailer side is new)

Eduardo R. profile picture

Eduardo R.

10/15/2024

You are a life saver ????

Carson K. profile picture

Carson K.

1/23/2025

I have break light on my trailer but no marker light. On my 2003 Chevy. When I hook up with my 2019 Chevy everything works. Why is my 2003 Chevy not giving power to marker light but power to my break light?

Jon G. profile picture
Etrailer Expert

Jon G.

1/23/2025

@CarsonK Your marker light is on a different circuit than your brake/turn trailer signals so odds are your 2003 Chevy has a fuse that needs to be replaced. Look in your manual for a fuse labeled "trailer running light" and check it/replace it to see if that fixes anything. If you're still having this issue with a good fuse in place then you'll want to check the wiring behind the trailer plug and see if it's been damaged in any way. Let me know what you end up finding out! I'd love to hear about it!
Carson K. profile picture

Carson K.

1/23/2025

@JonG Thank you so much, I'll check that fuse out and see what I find
Jon G. profile picture
Etrailer Expert

Jon G.

1/23/2025

@CarsonK You're welcome!
Randy S. profile picture

Randy S.

3/3/2025

I have a 2010 Ford F-150 XLT. My trailer lights were not working. Turn signals work when hooked up to truck trailer 4 pin connector. The problem was Relay for Trailer Tow Park Lamp Relay was bad. This is Number 6 in Fuse box in engine area. Hope this helps someone.

Jameson C. profile picture
Etrailer Expert

Jameson C.

3/3/2025

@RandyS I'm sure it will! Thanks for passing that on!
Robert profile picture

Robert

5/2/2025

I had all lights working and trailer all finished up all my marker lights worked i plugged truck in and my rear tight taillight was the only one not lighting up with truck lights on so I tried to diagnose it and blew my ram 1500 30 amp trailer fuse so I went and replaced it and now I have no marker lights at all but still have brake turn and hazards This is so frustrating and no online fuses in trailer wiring

Jameson C. profile picture
Etrailer Expert

Jameson C.

5/12/2025

@Robert Which specific fuse blew?
Robert profile picture

Robert

5/12/2025

@JamesonC it was the 30 amp little micro pink fuse mini square with the looking glass on top. I can't remember the 2018 dodge ram fuse position number but that one. Replaced it and now I get no marker lights when before I had them working except the right turn signal. And now the trailer plug tester middle top light that reads TM doesn't light up when I turn my daytime or headlights on. I find it weird that they worked then fuse blew and now nothing but brake and turn signals and no markers. I did run power to them and they all light up just not when plugged to truck.
Jameson C. profile picture
Etrailer Expert

Jameson C.

5/12/2025

@Robert I'd be willing to bet something went wrong in the TIPM which unfortunately only a Ram dealer can reset that. TIPM stands for totally integrated power module.
See All (5) Replies to Robert ∨
Tim profile picture

Tim

5/7/2025

I replaced the lights and wire on boat trailer (aluminum trailer). I have brake and turn signal but no running lights. Thanks

Charles H. profile picture

Charles H.

8/18/2025

I have replaced the wiring harness on my trailer. My truck running lights work and turn on. I have blinkers and turn signals on my trailer but not running lights…. I re did the ground connections for the trailer, still no running lights. I’m stumped can you give me any advice on where to go?

Jameson C. profile picture
Etrailer Expert

Jameson C.

8/18/2025

@CharlesH Did you test for voltage on the brown wire pin of the 4-way coming from the tow vehicle to make sure the circuit is active at all?
Joey profile picture

Joey

9/18/2025

My front trailer lights work. The rear doesn't. If I take out left side rear light and touch two post together lights work, until you touch brake then they go back out. I have replaced the rear three post plug for that side. Still doing it. Any thoughts?

Jameson C. profile picture
Etrailer Expert

Jameson C.

9/18/2025

@Joey It sounds like a weak ground on your trailer wiring. I would first check to make sure the ground pin of your trailer wiring connectors is clean and also go over the wiring of trailer and clean up any issues with wiring you find like loose wires or cut wires.

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