Troubleshooting Head Lights on Vehicle Causing Trailer Lights Not to Work

Question:

LED trailer lights so When I use the head lights on my vehicle I have no trailer lights no running lights turn signals break lights ect. However when the vehicles lights are off all the trailer lights work and everything runs fine. What is going on here? I’ve already tried hooking it up to 2 other vehicles and it does the same thing and have also cleaned the ground connections. If it helps any the trailer has a 4 prong pig tail and all three cars have a 7 way hook up I have also tried to different 4 to 7 way connectors and it does not change the outcome

asked by: Brett B

Expert Reply:

If you are turning on your vehicle headlights and the lights on your trailer are not working, and you did this with your other vehicles the issue is on the trailer and is almost certainly the ground. I know you said you cleaned it already but you also want to double check to ensure the ground wire is attached securely to the trailer frame via ring connector. If your trailer has a folding tongue, put the ground connection on the main body of the trailer frame and not the tongue; it should also not be attached to any aluminum section of your trailer.

Sometimes this can be the cause of an overload, though that shouldn't be the case with LEDs, unless you have a LOT of running lights. I have added links to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at.

expert reply by: Kyle S