Troubleshooting Hopkins Trailer Wiring Harness on a 1999 Toyota Tacoma

Published 09/13/2018

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Question:

Hi, I installed Hopkins 43315 four flat wire harness on my 1999 Tacoma and Im using 48655 four flat tester to test the system. With my headlights off, the tester shows the brake lights work and the turn signals work. When I turn on my headlights, only the tail lights work, the brake lights and turn signals stop working. The harness is cleanly and tightly grounded to the frame. Any ideas how to fix this? Thank you

asked by: Hanna

Helpful Expert Reply:

What you're describing is a textbook ground problem. The ground connection isn't strong enough to handle the load with the running lights on but will handle it when it's just the brake or turn signals. But you said your ground is good.

In this case make sure the pins of the Hopkins # HM43315 are clean and corrosion free. Also check the tester, especially the ground. I'd also check the connector with a trailer instead of just a tester or check the tester on another vehicle's 4-way. My guess is the tester isn't getting a strong enough ground connection.

Using a light tester, like part # PTW2993, might be a better option as well.

expert reply by: Charles S