2005 Jeep Wrangler Left Brake Light Stays On All the Time When Connected to RV

Question:

A problem with my towed vehicle, a 2005 Jeep Wrangler Unlimited, just cropped up and I need your opinion as to the cause and how to repair the problem. When I plug up my red wiring harness connector, 7 pin to 6 pin coiled jumper wiring adapter, the left brake light on the vehicle being towed illuminates and constantly remains lit. The left turn signal is inoperative as well. The right brake light, tail light, and turn signal, function properly. What may be causing the left brake light to be lit upon making the connection from my tow vehicle to my flat towed Jeep? Is it possible one of the diodes on the left side has gone bad? I look forward to your reply.

asked by: Andrew P

Expert Reply:

To determine where the problem is I recommend having the 2005 Jeep Wrangler Unlimited plugged up to the RV and then use a circuit tester such as # PTW2993 to test the wiring starting at the RV. You are looking for constant power on the left brake light/turn signal wire. Start at the RV and work your way back until you find the problem.

If it doesn't show up until after the diode, then that could mean that the diode is the problem.

Also, if you are using a supplemental braking system and the diode kit you have is the 4-diode kit then you will need to install the brake light relay # RM-88400 to prevent the Jeep brake signal from overriding the turn signal from the RV.

Otherwise, it sounds like a short that could be due to an exposed wire or connection touching another wire that has power. If that is the case, then fixing or replacing the wire should solve the issue.

expert reply by: Michael H