Trailer Wiring Issue

Old 05-21-13, 06:20 PM
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Trailer Wiring Issue

I recently purchased and installed a Curt wiring harness for my 2008 Corolla and have had some issues with the trailer. When I brake, only the right tail light illuminates. When I turn on the headlights, neither illuminate. Both turn signals work, but when braking and using the left turn signal, the left light goes off completely. The harness appears to be grounded to itself and the instructions don't indicate that grounding is necessary. Any tips?
Old 05-21-13, 06:46 PM
Tolyn Ironhand's Avatar
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Welcome to the forums!

With trailer lights, ground is quite necessary, otherwise your lights will not work.

Your 12 volt system uses positive and negative (ground) for a complete circuit. Most cases there will be only one wire going to each bulb, or element inside the bulb. So on a left tail light, you will have one wire for break/turn, and one wire for running lights. How does the bulb work with one wire? They use the frame of the trailer as your return path. The trailer, and metal frame of the car, is negative (ground) and connected to the negative terminal of the battery/electrical system.

Make sure you have a good ground on your trailer. At one time, they would just expect the trailer sitting on the ball would good enough. Its not. Now they will carry a ground wire (most cases the white wire on the wiring connection) and connect it to the trailer frame. Check all the ground connections from the wiring connection on the trailer, and the ground connection at each light.

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