Trailer Taillights Malfunction When Vehicle Headlights are Switched On  

Question:

Expert Reply:

What you're describing is the classic symptom of a ground problem. Everything works fine until the headlights are turned on, which is when the maximum amperage is drawn through the system. That's when a ground problem will rear its ugly head.

On the vehicle side of the equation, there's a white ground wire exiting the converter box. Make sure that's connected to clean, bare metal on the vehicle. If there's any corrosion or undercoating or dirt that's preventing the back side of that ring terminal from contacting bare metal, it could lead to an insufficient connector. The threads of the self-tapper provide somewhat of a connection, but not always enough for everything to function properly.

I've linked you to our trailer wiring troubleshooting article, you might find it helpful.

Next, look at the trailer connector on the trailer. Locate and follow the white ground wire from the connector and find where it grounds to the trailer frame. Make sure that connection is good and tight, once again, with no corrosion. To make it super-bulletproof, I like to take out the ground screw and sand a dime-sized area round the hole for the ground screw down to bare metal. Get a star washer, and install that between the ground connections ring terminal and the trailer frame. When you run that screw down, that star washer will really bite into the metal, ensuring a good connection. I like to give the ground screw a quick shot of rust preventative spray paint to protect it.

Next, check each trailer lamp. Each lamp will either ground via its mounting stud or by a separate ground wire. Make sure all those connections are tight and not rusted.

It might take a little time, but once you get those grounds clean and secure, everything will work fine again.

expert reply by: Mike L

0