Troubleshooting Tail Light Outage On Trailer Where All Other Functions Work  

Question:

Expert Reply:

I recommend starting with checking your trailer ground wire. The ground is often at fault when only one function is not working correctly. Make sure your ground wire to your trailer frame is free of corrosion and rust. It should be a bare metal to bare metal connection. If that ground is good, check to see if your trailer lights are grounded by the hardware. This is sometimes the case and then either requires bare metal to metal at the mounting hardware or requires a jumper wire to a better ground.

If that doesn't solve the issue, then I recommend using an incandescent circuit tester like # PTW2993 to test your functions at your vehicle before the trailer is connected. This will isolate the issue to the vehicle or trailer. If the vehicle is the issue, you may need to replace your vehicle wiring harness since your fuses are good.

On the trailer, make sure the connection to the vehicle is good with no bent pins and is also clean of corrosion or debris. Then use just a battery to test your trailer wiring using the negative terminal connection to your trailer frame and the positive terminal with a short jump wire to test each function. If everything works, you need a new ground location. If this doesn't work, you will trace the wires on each side to your taillights checking for function along the way. Since your turn signals and stop lights use this same wire, it is rare this is the issue, but if you find a short, replace that portion of wire.

expert reply by: Jason S

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