Back Up Lights Come On when the Power Wire On the Trailer is Connected to the Center Pole

Updated 01/12/2010 | Published 01/11/2010

Question:

I have a 1999 Chevy truck wired with a 7 blade style connector for my camper. All work fine including center pin used as a charging line for the camper battery on my camper and several others that I move around from time to time. Recently tried to fix a friends dump trailer wiring and all is fine except I tried to run a hot line from my center connector with a new wire directly to his battery so it can be charged while driving to dump trailer, this was not included from trailer manufacturer. When I added this wire from trailer center pin to the battery, the backup lights on my truck come on with the trailer hooked up. When I remove only this one new wire, the trucks backup lights go off. All else seems fine as I usually maintain this trailer for this person. Any advice.

asked by: Dennis S

Expert Reply:

I would start by using a circuit tester, item # PTW2993, to check the center trailer connection on the truck. If you have constant 12-volt power on this circuit, then you are correct that it could be used to charge the battery on your trailers and the dump trailer.

With the reverse lights coming on when you hook up the trailer with the battery connection from the dump trailer connected to the center connection, I believe that you may find that the center pole on your trucks 7-way connector is connected to the reverse light circuit. To check this, have someone shift the truck into reverse, with the emergency brake engaged and their foot on the brake and the tester connected to the center pin. If you get power, you will know for sure that the reverse circuit is connected to the center pole. In this case, the 12-volt charging connection should be in the 1 O-Clock position when looking at the vehicle side 7-Way with the cover raised. Check this connection with the circuit tester and you should have constant power. We have a diagram that shows the 7-Way connections for you to review (see link). If this is the case, then the power wire to the trailer battery should be connected to the connection in the 11 O-Clock position on the trailer connector looking at the connector from the outside.

expert reply by: Robert G