Finding Cause of Brake Lamp on Challenger 5th Wheel that Illuminates when Running Lights are On  

Question:

Expert Reply:

The first step is to determine if the problem is on the vehicle or the trailer. Use a circuit tester like part # PTW2992 on the pins of the trailer connector on your truck. Have a helper activate each lighting function as you test the pins on the connector to ensure that the correct pins are getting power while the correct function is activated. The Trailer Wiring help article I've linked you to shows which pin should carry which function. If the running lights are switched on, you shouldn't be getting any power on the pin in the 3:00 or 9:00 position.

If you find the problem to be in the vehicle wiring, check the trailer connector in the bed of the truck, as well as where it taps into the vehicle wiring under the vehicle. Corrosion in the trailer connectors would be the prime culprit for what you're describing. If you're getting the proper signals on the trailer connector when you test it, next examine the connector on the trailer.

Closely examine the sockets on the connector, looking for green or white corrosion on the brass contacts. If you find any corrosion, there's a good chance that corrosion has spread to the interior of the connector and is causing the right brake lamp and the running light signals to interfere with each other. Trace the right turn circuit back to the lamp, looking for pinched wires or loose connections. At the lamp itself, check the bulb and the socket it fits into. Excessive corrosion could also be causing your problem.

expert reply by: Mike L

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