How to Wire New Trailer Taillights with Two Black and One Red Wire

Updated 10/27/2009 | Published 10/26/2009

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Question:

I have two black wires and one red wire coming off each new tail light but nothing to tell me what the wires are for. Can you help with that? Also, I get only tail lights, no brake lights or turn signals. Any ideas.

asked by: Mike B

Expert Reply:

Of the three wires, one would be the ground, one for the turn signal/brake light, and the third for the running lights. I am not familiar with the wire colors you describe. Your best bet would be to connect to the existing wires in differing combinations until the lamp works correctly.

The first step in diagnosing the wiring problem would be check the wires leading to each fixture to ensure that the signal is getting through. Typically, there will be a yellow and a brown wire on the driver's side, and a green and a brown wire on the passenger side. Use a circuit tester such as part # PTW2993, to verify that the proper signal is reaching the attachment points for each lamp. If you are not getting a signal on the green or yellow wire on each side, you will want to test the trailer connector on the vehicle to make sure the signals are properly leaving the vehicle. Check the connector itself to ensure it is not corroded or damaged.

expert reply by: Mike L