Trailer Brake and Turn Signals Not Working When Connected to a 2008 Ford F-250

Updated 07/31/2018 | Published 07/30/2018

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Question:

I have an 08 f250 that I pulled my trailor with. Just recently found out that my running lights works fine but none of the signal or brake light work... I check the fuses and even replace a relay. Any other idea that I might have missed?

asked by: Sam

Expert Reply:

There is a fuse for the trailer stop/turn relay on the 2008 Ford F-250 in location 34 under the hood. The relays are in location 20 and 21 and the easiest way to test those is to use a known good relay in place of a potential bad one. But it might not even be an issue on the truck side.

To know for sure where the problem is coming from you can use a circuit tester such as # PTW2993 or a meter if you have one to test the connector on your truck. If the turn signal and brake lights are working at the connector (3- and 9 o'clock positions on a 7-Way) then the issue is on the trailer side.

If there isn't power when there should be on those pins, then the issue is on the truck. Aside from checking all possible fuses and relays you can inspect the wiring going to the connector as well as clean out any corrosion inside the connector, where the wires attach, as well as on the pins.

If you determine the issue is on the trailer side, make sure that the trailer's connector is clean and free of corrosion inside and out. Make sure that the main trailer connector ground and the grounds for all of the trailer lights are attached to clean bare metal surfaces.

expert reply by: Michael H