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Trailer light issue

I have an 02 Trac (09-01) and have turn and brake lights on the trailer, but no trailer running lights. I have checked the fuse and relay. I have power at the relay, and coming out of the relay, but at the plug under the cab where the harness leaves the interior and enters the frame, I have no power at the plug (brn/w) I have applied power to the frame side of the plug and get the lights to light on the trailer. So I'm losing connection between the trailer tow relay (auxillary box 2 under the dash) and the frame plug under the cab. Is there another plug between the relay and the frame plug before I go ripping the interior out finding the open circuit? Keep in mind I am not blowing any fuses, so its not a short. Thanks for the help...



Well-Known Member
January 22, 2010
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City, State
Indian Mound, TN
Year, Model & Trim Level
02 V8 Sport Trac 4x4
Small update. I had a little time to do more diagnosing. On the back of the auxillary relay box 2, I have power coming into the trailer tow relay, and output power is off when lights are off, and I get 12 volts when the lights are on, so the relay is functioning. I start tracing the harness down, starting from the plug below the cab. It enters the cab under the driver front seat. To my surprise, it doesn't run forward, it runs to the back of the cab. From there it runs under the seats to the passenger side. At the passenger rear cab corner the trailer light circuit doesn't continue, so somewhere between the driver and passenger rear cab corners the circuit splits from the rest of the harness. There are two splits, one on each side going up behind the seats, but it doesn't run with either split. With no visible harness exiting under the cab, and not having time to pull the seats to expose the rest of the harness, I figure it must run up the center with the center console harness. I pull the front top section of the console to expose the wiring harness at the dash, to my surprise the circuit is not there. So I put the truck panels back together and quit for the evening as I had other things I needed to get done. The search continues...