Brake and Turn Signals do not Work When Headlights Come on

Question:

Help!! So I have an 02 Chevy express and I added a Hopkins trailer towing harness on it with a converter switch because I have independent turn and brake lights and my trailer has a single light with combined functions and now on my trailer I get brakes and signals but as soon as I turn on my headlights and taillights I only get fully lit lights on my trailer...no signals or brakes...I have checked all my grounds and connections and now I’m at a loss...when I test my harness on my van with a trailer test light everything test out ok...? Any advice would be very helpful!!

asked by: Lloyd C

Expert Reply:

There are a couple of possible issues happening and you were right to check the grounds and ensure your connectors were okay.

Did you test your wires coming into and going out of the harness? 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.

Also, even if your grounds are good, you will want to make sure each tail light has its own ground and take a close look at the wires - including the ground wires - to ensure none are crimped, broken or otherwise damaged. There may also be an overload, so check the maximum amperage rating of your harness and determine the amperage draw of your trailer lights to confirm that lights do not draw more power than the harness can handle.

I've also added a help article for you on troubleshooting trailer wiring which I recommend checking out.

expert reply by: Kyle S