Troubleshooting Trailer Lights on an Older Trailer and a 2004 Chevy Tahoe

Updated 01/09/2012 | Published 01/06/2012

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Adapter 7-Pole to 4-Pole and 5-Pole

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Hook Probe Circuit Tester

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Question:

I have a 2004 Tahoe and an older trailer with a 4-pin connector....I am assuming the Tahoe s factory plug is a so called 7-flat blade plug...?! I bought a 7-flat blade fits in to 4 pin addapter...plugged in and now the signal lights act like emergency blinker, the trailer brake lights go off when I push the brakes on the Tahoe....park lights work and regular taillights work too...whats wrong??

asked by: James P

Expert Reply:

There are two possibilities for the problem you are experiencing. Either the wiring on your 2004 Chevy Tahoe is incorrect, or the wiring of your trailer is bad.

The first thing I would do is test the 7-way on your Tahoe by function to determine if it is the problem. To do that you will need a buddy to apply the different brake and taillight functions of your vehicle while you test for the correct voltage with a Circuit Tester like # PTW2993 on the 7-way. I attached a video on how to do this with a 4-way for you to check out to give you the basic idea of how it will work. I also attached a picture of a 7-way that shows the correct way it should be wired for you to use as a reference.

If you determine that the problem is in the Tahoe wiring, you will need to check the wiring of the 7-way for loose or exposed wires and fix as necessary. It sounds to me like there are some circuits that are shorting out onto each other and causing the bizarre behavior you are describing.

Or if you have access to another vehicle with a 4-pin connector you could connect that vehicle to your trailer and see if the same problem arises. If the problem goes away you know it is your Tahoe, if not then the problem is in the trailer. If you find that it is in the trailer check out the FAQ I attached that shows how trailers are typically wired that you could use to trouble shoot your trailer. You will want to make sure that everything is wired up correctly. You may find that the 4-way on your trailer has the pins wired differently, or there is a short on the circuits.

You will also want to make sure there are no ground problems either as ground issues can cause all sorts of strange problems. The ground wires should be attached to clean metal surfaces.

expert reply by: Jameson C