Troubleshooting Trailer Brake Lights Not Working on a 2003 Chevy Silverado 1500


I have working running lights as well as turn signals however I have no brake lights. What should be my next steps? Thank You! One other note the lights on the truck are all working.

Expert Reply:

Since the lights on the truck are working but the lights on the trailer are not, I am inclined to believe that the problem is on the trailer side but I do not want to rule out the truck just yet. First, I recommend testing the trailer connector on the truck side. You will need 2 things. First, you will need a circuit tester like # 3808 if you do not already have one. Second, you will need someone to sit in the truck to run the lights while you test the trailer connector.

The brake lights and turn signals share the same circuit. So if you are looking at the face of the plug on a 7-Way, the pin for right turn and brakes is in the 3 oclock position. The circuit tester should light up solid when the brakes are pressed and blink when the signal is on. Next, do the same with left turn/brake at the pin in the 9 oclock position.

If everything is working properly, you can eliminate the truck. If the tester does not light up with the brakes pressed or it lights up on a different pin, then something is not wired correctly or there could possibly be a fuse or relay that needs to be replaced. The owners manual can tell you the location of the fuses and relays.

While at the truck side connector, if you find any corrosion or dirt, go ahead and clean it out. Do the same with the trailer side connector. On the trailer side connector, make sure that the main ground is connected to a clean and corrosion free bare metal surface. Trailer lights usually ground through the mounting studs and they, too, will need to be attached to a clean and corrosion free bare metal surface.

expert reply by:
Michael H

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