Troubleshooting Wiring on a Fifth Wheel Trailer With No Tail Light Function  

Question:

Expert Reply:

Your best course of action is going to be a systematic check of the wiring, starting from the front of the truck to the rear of the trailer. It will take some time, but you will find the problem this way. I suspect the problem is on the trailer, most likely somewhere between the side markers and the tail lights. However, the vehicle can be checked quickly and if the problem is there it could save a lot of time

Start at the front of the vehicle by checking fuses. Your vehicle owner manual should show diagrams of the fuse blocks and list what does what. Check any fuses involved with the 7-Way or truck tail lights. If all the fuses look good, then it is time to move to the rear of the truck and start checking the 7-Way.

Use a circuit tester, like part # PTW2993, to check the contacts in the 7-Way for proper function. I have included a wiring diagram page that shows how a 7-Way should be wire. Make sure that functions at the connector match what is listed in the diagram. If everything on the vehicle side checks out, then the problem must be with the trailer wiring or lights themselves.

From the way you described the problem, it sounds like the only function that is having trouble is the tail/running light function, but only on the rear tail lights. I imagine the problem is between the side markers and the tail lights. If you have a mix of LED and incandescent lights, you may have burned up the LEDs as incandescent lamps draw much more amperage than an LED can handle. Follow the wires from where the side markers attach to the circuit and follow them back to the rear tail lights. Check for frayed wires or loose connections.

If you do not find the problem, please write back and let us know what you found and we can go from there.

expert reply by: Patrick B

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