Troubleshooting Running Light Not Working on Trailer  

Question:

Expert Reply:

I was unable to find the wiring harness you purchased from us to give you any specificity about that, but I can give you some general troubleshooting tips which should remedy the malfunction of your trailer clearance lights not working. My best guess is a bad ground, as this is the issue virtually every time, so you'll also need to make sure your grounds are attached to bare metal surfaces and free of any paint, dirt or corrosion. I'm guessing this will clear up the problem.

If it doesn't, since you already checked fuses, in order to determine the specific problem you will need to purchase a circuit tester if you do not have one - the very handy Cordless Circuit Tester # PTW2979 would be my strong recommendation due to how easy it is to use - and test the connector on your vehicle after disconnecting it from your trailer. Check the wiring going into your harness from your tail lights to see if those wires are carrying the correct signals, if not then the issue is with the vehicle wiring.

If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring. 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.

Additionally, I also highly recommend using Dielectric Grease for Electrical Connectors # 11755 to help prevent any type of corrosion in your connector; using it will increase your 4-way's durability and extend its lifespan.

expert reply by: Kyle S

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