Trailer Connected to 2012 Ram 2500 Causes Truck Reverse Lights to Come On

Published 10/27/2014

Question:

I have a 2012 Ram 2500 with the factory installed harnesses. I have towed a boat with a 7 pin harness and surge brakes with no issues. I purchased a 2007 Mirage Balboa toyhauler with electric trailer brakes and now have 2 problems. When I connected the trailer, the back up lights on the Ram turned on and stayed on. I put the truck in reverse and they stayed on. I checked for corrosion and saw no obvious signs of it in either harness. The lights stayed on the entire time I pulled the trailer home from the purchase. I noticed when I was connecting the trailer that there was a very small spark from the center pin when I bumped it against the steel hitch. I just happened to bump it into the steel hitch by the ball and see the spark while I was troubleshooting the reverse lights on the truck. I disconnected the house batteries in the trailer, and the spark still was there. It remained a very slight spark, but it was there. I had no issues with the truck or trailer pulling it home, other than the reverse lights staying on. Do you have any idea what would cause these 2 seemingly related issues?

asked by: Arnold M

Expert Reply:

The center pin on your 2012 Ram 2500 is probably wired to the reverse lights. The center pin on the trailer is probably wired to a trailer mounted battery or breakaway system battery and it is back feeding to the trucks reverse lights.

The trailer could have more than 1 battery on it. What you will need to do is figure out what is wired to that center pin on the trailer side.

I have included a picture that shows the pin out functions of a vehicle side and trailer side 7-Way that should help. Ignore the colors of the wires and focus on just the functions.

expert reply by: Michael H