Troubleshooting Utility Trailer Taillights Stop/Turn Signals Not Functioning

Question:

I have a 1999 jeep Cherokee with a c55354 wire harness installed. the trailer and the harness are all new and never used before. I have power before and after the converter every time. when the trailer is plugged into the harness I have running lights but no brake or turn signals. I took a 12v car battery and wired each lead to the trailer and each connection worked every time. so the trailer wiring seems to be working fine. I then hooked the trailer back to the jeep, the power after the converter goes off. but only when the trailer is plugged into the harness. when I unplug the trailer the power works again after the converter. this problem makes no sense because I tried a different converter harness and I had the same problem. is there a defective problem with the converters being used on a jeep Cherokee. what should I do.

asked by: Ben H

Expert Reply:

It sounds like the problem is the trailer's wiring. I know it may seem like it is working correctly since you powered it with a 12 volt battery and it appeared to work like it should, but what is most likely the problem is either from having a weak ground on your trailer wiring or the trailer lights are drawing more power than the trailer wiring is rated for.

Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light. Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also 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.

If improving the grounding of the assemblies doesn't fix the problem then the issue is that the lights are drawing too much. A very easy solution to fix this problem is to convert the taillights of the trailer to LEDs as they draw a fraction of the amperage that an incandescent bulb draws.

I attached a couple FAQs on trailer wiring that you may find helpful as well.

expert reply by: Jameson C