No running lights on trailer

[homedad]

I have no running lights on 2 trailers. I know it’s the truck because it’s 2 different trailers and I’ve used one of those test plugs with leds. I’m not sure which fuse or would be. I welcome any replies. BTW I still have electric brakes, both turn signals and brake lights.

 

[Sascwatch]

If your lights are set to auto the running lights will only be lit when the truck thinks it’s dark, have you tried turning the lights to a different setting?

If you did and it made no difference I’d check fuse F12.

 

[millerbjm]

If your lights are set to auto the running lights will only be lit when the truck thinks it’s dark, have you tried turning the lights to a different setting?

If you did and it made no difference I’d check fuse F12.

2nd this - I always turn the dial to on when towing to check that running lights are working and often just drive that way as I like the extra lights when towing.

 

[Richard320]

Check F12 in the underhood fuse box.

There are spare fuses around the perimeter. The one you'll need, if it's blown, is kinda above F32 and F45. Unless someone has moved it.

 

[homedad]

Yes I’ve tried turning the switch to headlight and not just automatic. I looked at J12 but only visually. I’ll look for a spare. Thanks all.

 

[Ratchet]

Assuming you're talking about the 7 way plug? The test plug is showing the parking circuit dead as well? Remove trailer light tester and test the pin for parking lights directly inside the 7 way with a volt meter or 12v test probe. Most likely it's the plug on the truck. The pins have been known to slide back into the connector just enough that it doesn't allow a good connection between the two. Have seen this generally on the brake light circuit and parking light circuit on quite a few vehicles. Been there, done that. Bought a new 7 way. 2 min install. Have part numbers if you need it.

 

[Rlaf75]

Use a test light to see if you're getting power to the back side of the trucks connector. Then see if the front side has power.

 

[Wildhawk107]

I had the same issue, the truck seemed good, fuses were fine, trailer worked when connected to other brand trucks but not on my 2025 Ram Rabel.

Ram said it was the trailer, the trailer shop said it was Ram. It turns out that there were too many incandescent running lights for the truck to handle and it was throwing a code and turning them off as a safety feature.

Try removing the bulbs from your trailer and reinsert them one at a time to see the number of bulbs your truck can handle. I could run all but 2 of mine. My solution was to replace the center rear 3 running lights with one LED strip which lowered the draw enough for all to work without issue.

 

[jonusko]

I had the same issue, the truck seemed good, fuses were fine, trailer worked when connected to other brand trucks but not on my 2025 Ram Rabel.

Ram said it was the trailer, the trailer shop said it was Ram. It turns out that there were too many incandescent running lights for the truck to handle and it was throwing a code and turning them off as a safety feature.

Try removing the bulbs from your trailer and reinsert them one at a time to see the number of bulbs your truck can handle. I could run all but 2 of mine. My solution was to replace the center rear 3 running lights with one LED strip which lowered the draw enough for all to work without issue.

This just happened to me on my 2025 Laramie. The trailer running lights would come on for a split second and go off. We started replacing the incandescent trailer lights with LEDs and then lights came on and stayed on. I am not happy replacing all of the lights, but at least it’s working now.

 

[Bt10]

Just experienced this today myself. Have to start digging tonight.

 

[Bt10]

Where/how is the code displayed?

 

[Bt10]

Fuse blown. No idea how or when. Lights working now, hopefully stays. My fuse drawer is getting quite diverse now.

 

[alinl]

Similar issue here – 2025 RAM 1500 with a 1999 Wells Cargo trailer – all lights are incandescent lights. Turn signals and brake lights are working perfectly, but no running lights (about 20 bulbs on running lights). I disconnected all but tail and tag light and works just fine now.

The behavior of the truck was as follows: connecting the trailer would start light tests followed by an error with the message “check trailer connection”. I used the trailer on a BMW X7 without any issue. I switched the cars and connected the trailer to X7 – sure enough worked. Connected back to RAM and got same error. Checked the interior fuses (days before I installed a dash cam and I was afraid I messed up something) and fuses were all OK. Since I had no another trailer to test the truck, I continued to research and troubleshoot.

I started to check the receiver on the truck and all was wired correctly. Started the truck and engine and I measured the voltage on the pin dedicated to running lights and I had 13+Volts. Connected the trailer and failed with same error, disconnected the trailer while the engine was still running and measured the voltage on the same pin as before – had only residual power, about 1V or so. Stopped the engine and started it and the voltage on the pin was back to 13+V. Connected the trailer and the power was lost.

Considering the pattern I discovered, I initially suspected a short, but the BMW was fine and I drove the trailer over very long distances without any issues, so I ruled that out and all left to suspect was an incompatibility. I kept researching online and run into this post which opened my eyes – I disconnected all wires corresponding to running lights in the trailer hub then identified the tail and tag lights. Connected only these and sure enough the trailer lights are working flawless now.

Conclusion is that the trailer limits the current draw via software which I do understand. What I do not understand why they designed this mechanism considering only LED lights? My trailer is 25+ years older, but I am sure it will outlast the truck due to its build quality. The designers need to consider backwards compatibility and not think that everyone that buys their truck has a newish trailer.

 

[Pikeman_66]

Similar issue here – 2025 RAM 1500 with a 1999 Wells Cargo trailer – all lights are incandescent lights. Turn signals and brake lights are working perfectly, but no running lights (about 20 bulbs on running lights). I disconnected all but tail and tag light and works just fine now.

The behavior of the truck was as follows: connecting the trailer would start light tests followed by an error with the message “check trailer connection”. I used the trailer on a BMW X7 without any issue. I switched the cars and connected the trailer to X7 – sure enough worked. Connected back to RAM and got same error. Checked the interior fuses (days before I installed a dash cam and I was afraid I messed up something) and fuses were all OK. Since I had no another trailer to test the truck, I continued to research and troubleshoot.

I started to check the receiver on the truck and all was wired correctly. Started the truck and engine and I measured the voltage on the pin dedicated to running lights and I had 13+Volts. Connected the trailer and failed with same error, disconnected the trailer while the engine was still running and measured the voltage on the same pin as before – had only residual power, about 1V or so. Stopped the engine and started it and the voltage on the pin was back to 13+V. Connected the trailer and the power was lost.

Considering the pattern I discovered, I initially suspected a short, but the BMW was fine and I drove the trailer over very long distances without any issues, so I ruled that out and all left to suspect was an incompatibility. I kept researching online and run into this post which opened my eyes – I disconnected all wires corresponding to running lights in the trailer hub then identified the tail and tag lights. Connected only these and sure enough the trailer lights are working flawless now.

Conclusion is that the trailer limits the current draw via software which I do understand. What I do not understand why they designed this mechanism considering only LED lights? My trailer is 25+ years older, but I am sure it will outlast the truck due to its build quality. The designers need to consider backwards compatibility and not think that everyone that buys their truck has a newish trailer.

I have the same problem with my boat trailer. A leds too. Every light works except the running lights. Light work just fine on buddy’s truck (non Ram) there is a problem with the 2025s light circuit or software and they aren’t addressing it!!
I am pretty poed at this point I tow my bass boat in the early dark hours and I am having to run Hazards of all things!!