How to Troubleshoot Turn Signals on Trailer Not Working  

Question:

Expert Reply:

The # 33355 trailer wiring harness you purchased receives its ground connection from its connection to the vehicle, it doesn't need a separate ground connection. The easiest way to test the harness would be to try plugging another trailer into the vehicle, then try another vehicle with the trailer. This will immediately tell you where the problem lies. If this isn't possible, I'll walk you through some troubleshooting strategies.

When you have trailer lights acting up, the first thing you'll want to do is test the trailer connector using a circuit tester like # PTW2993. Have a helper activate the turn signals as you test the sockets on the trailer connector. The socket fed by the yellow wire should light the tester up when the left turn signal is activated, or the brake pedal is pressed. The socket fed by the green wire should light the tester with the right turn signal and brake pedal.

If you don't get signal, check the connections where you plugged inline between the vehicle's wiring harness and the taillight assemblies. Make sure the connections are fully pushed together until they click. If you still get no signal with the tester, the wiring harness is faulty and should be replaced.

If you do get signal on the turn signal/brake lamp sockets, then the problem is in the trailer wiring or the lamps themselves. Since neither turn signal works, a ground problem is the most likely possibility. Make sure the trailer wiring harness is securely grounded to the trailer frame. The main ground us usually on the trailer tongue. Make sure the connection is tight and not corroded. The trailer lamps themselves should be grounded to the trailer either by a separate ground wire attached to the trailer frame or by the lamp mounting studs being directly mounted to the trailer frame. These connections also need to be tight and rust-free. If the trailer has a tilting or pivoting tongue, the connection at the pivot could be worn to the point where the ground connection is poor. Try using a short length of wire with two ring terminals on the ends to connect the tilting tongue to the rest of the trailer to make a continuous ground.

Run through the suggestions above. I'll also link to a trailer wiring troubleshooting article that you might find helpful. And don't forget to let us know how it works out!

expert reply by: Mike L

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