Troubleshooting Trailer Running Light Problem on 1991 Terry Resort Trailer

Question:

Hi There The running lights on my 1991 Terry Resort trailer dont work at all while hooked up to my 2010 Ford F150 Platinum. When I am parked at a campsite and I bridge the positive to the running lights on the trailer harnesspicture, only some of the lights work, but when I hook up to my truck, I have no luck with any lights. While towing, the signal and break lights work... thankfully, but that doesnt help when its dark out, causing me to time my trips in the light, which doesnt always happen. I have recently re-bored holes in the trailer frame and cleaned all the ground connections etc... I have tested all the bulbs one by one to see if they work... and they do, and yet no luck. I am at the point where I think I need to spend some $$$ to get it done professionally.

asked by: Gary C

Helpful Expert Reply:

It sounds like there is a simple solution, we just need to start at the beginning and work our way through it. I recommend using a circuit tester like # PTW2993 for this process. Let's start at the 7-way trailer connection on your truck when the trailer is not connected. Turn on your running lights on your truck and then use the tester to check the 11 o'clock pin on the trailer connection. This is the tail/running light function. If that works then you have isolated the issue to the connection between the truck and trailer or the trailer. If it doesn't work, then you have isolated the issue to the truck itself. Often there is a fuse for the trailer lights that you'll want to check your owners manual for. After fuses and relays being replaced, you get to a re-wiring situation and you can use the circuit tester to find the short as you trace the wire and test ever couple of feet.

If it is on the trailer, there is a really good chance it is the trailer ground. To test this, run a jump wire from your truck battery negative terminal to the ground on your trailer. If everything works when connected at that point, you need to create a better ground with bare metal to metal contact. You will need to check the ground on each light fixture that isn't working if they aren't connected to a common ground. Each connection needs to be bare metal to metal without corrosion, rust, or debris. Jump wires for positive and negative can test each light fixture individually if needed and then you can trace wires for a short and replace as needed.

expert reply by: Jason S