trailer brake light problem

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Sep 14, 2013 | 02:34 PM

daerhldgs2

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Joined: Apr 2003

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trailer brake light problem

I have a 99 F150 with the 7pin tailer plug. When I don't have my running lights on all signals and brake light operate on the trailer, but with the running lights on when the brakes are applied the taillights on the trailer go out, when the brakes are released the running lights come back on, meanwhile the brake lights and running lights on the truck work properly. Any ideas would be welcome!

Sep 14, 2013 | 10:19 PM

Bluegrass 7

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Joined: Sep 2006

Posts: 7,907

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There is a poor ground at some point on the trailer.
Trailer power goes though relays from battery so an issue on the trailer does not affect the truck lights.
Good luck.