How to Get Interior Lamps Working on Cattle Trailer

Published 02/13/2016

Question:

what fuse do I need to look at to get the lights to work inside our trailer? All turn lights, running lights and brakes work fine but I can not get the interior lights to work on our cattle trailer. I just bought a 2016 ford f250 with tow package and gooseneck package. I had chevy before and they always had a dummy plug in the fuse box that needed to be replaced

asked by: Greg

Expert Reply:

Many times, the interior lights of a trailer are tied into the running light circuit, so you'd need to have the truck's headlights or running lights on in order for the interior lights to work. Sometimes they're wired into the auxiliary 12-volt circuit coming off the trailer connector. It sounds like your trailer has the lamps tied into the aux circuit, so you'll want to confirm that circuit is functioning by using a circuit tester like part # PTW2993 on the pin in the 1:00 position.

If there's not power on that pin, check the fuse box under the hood. The owner's manual states that the auxiliary circuit on the 7-way is protected by a 25-amp fuse in fuse location # 90. Also, make sure that the 40-amp fuse is in place in location # 10.

If neither fuse is missing or blown, the problem must exist in your trailer wiring. You'll need to trace the interior lamp circuit from the lamp to the trailer connector, looking for loose connections or wires that are pinched or that have cracked or worn insulation.

expert reply by: Mike L