With Trailer Connected Truck Reverse Lights and Trailer Brake Lights Are Not Working

Updated 03/18/2014 | Published 03/17/2014

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Question:

I have a problem with my 7way in my truck n my trailer when I plugit in the truck my back lights in my truck go deem the stop lights in the trailer dont work how can you help me please

asked by: Joe

Expert Reply:

It sounds like you might have a few different issues going on here. First, we need to test the vehicle side 7-Way connector to make sure it is working properly. Use a circuit tester such as # PTW2991 to test the pins on the connector while someone sits in the truck and runs through the light functions.

If something does not work then you will need to determine the problem. Check the trailer connector for corrosion inside and out. Corrosion can cause all sorts of issues, so can ground problems. If the connector ground wire is visible make sure it is attached to a clean and corrosion free bare metal surface.

On the trailer side, make sure its connector is clean and free of corrosion inside and out. Then make sure that the main trailer connector ground and the grounds for all of the trailer lights are connected to clean and corrosion free bare metal surfaces.

Another possible problem is amperage draw. If the trailer has a lot of lights on it then it could be drawing more power than what the tow package wiring on the truck is rated for. An easy way to test this is to disconnect a few lights. Then if everything starts working you know that it was either too much power draw or one of the disconnected lights is malfunctioning.

I have included a couple of links that should help. One is on trailer wiring and shows the configurations of various trailer connectors. The other is on troubleshooting wiring.

expert reply by: Michael H