Interior Trailer Lights are Not Working but All Exterior Lights Do Work

Question:

Help on getting interior lights working.

asked by: Russ

Expert Reply:

You will need to determine what circuit the lights on your trailer are connected to. If the lights are hooked up to either the 12-volt circuit on the 7-Way or the auxiliary power circuit, then it could just be a matter of making that function active on the vehicle side. If the lights go first to a trailer mounted battery, make sure the battery has a charge and that the power wire and grounds are intact. They can also be tied into the running light circuit so you would check it as well.

To check the 7-Way functions on the vehicle side, use a circuit tester like # PTW2993. The pin in the 1:00 position if facing the connector is the 12-volt circuit. The center pin is the auxiliary circuit though it can also be reverse lights. If power is getting through to these pins (or whichever pin the interior trailer lights are connected to) then you know the issue is a wiring problem on the trailer side.

But if there is no power on the vehicle side then you will need to check any fuses or relays related to the tow package wiring. Use the vehicle owner's manual to find their locations. If you happen to have a Chevy or GMC truck, there may be some connections under the hood you have to make to make everything fully functional.

expert reply by: Michael H