Troubleshooting Brake Light Issue with Modulite Wiring # C59496 on a Mitsubishi Endeavour

Question:

I installed the C59496 wire harness kit for my 2010 Mitsubishi Endeavour. I then connected my camper trailer. The running lights and blinker work. However, the brake lights are always on...on the trailer. I disconnected reconnected everything on both sides. This worked.....for about 10 minutes. Then the same problem appeared. I checked the voltage at each pin of the 4 pin connector and get 12 volts when the brake pedal is not engaged. The brakes lights on my car do not light up. Now neither one of brake lights work on y car. The 3rd top brake light does work. Did I short something out? Any help would be appreciated.

asked by: Mike R

Expert Reply:

Is it possible that a fuse is getting blown when you hook up the trailer? I would focus on the vehicle side of the equation to begin troubleshooting, without the trailer connected. This way you can start with a clean slate, and concentrate on getting the vehicle lighting back to functioning as it should.

To start, I would recommend disconnecting the black power wire from the # C59496 wiring harness from your vehicle battery. Then, disconnect the positive and negative cables from the battery on your 2010 Mitsubishi Endeavor, and leave them off for about 5 minutes. This should reset the computer and get you back to default settings.

Reconnect the battery cables and make sure that your vehicle lights are working as intended before moving any further. Then you can reconnect the power wire for the harness, but do not plug in your trailer. At this point, you will want to use a tester to see if the issue is still occurring. If you have constant power at the 4-Way plug on the yellow or green wires, or if your vehicle lights again stop working, the converter box on the harness is likely malfunctioning and would need to be replaced.

If everything is working as normal, the trailer is the most likely culprit. I would recommend that you check along the trailer wiring and make sure that there are no spots where the wires have gotten pinched or nicked. A bare spot could be touching the trailer frame and causing a backfeed situation.

It would also be wise to check all the ground wires or grounding hardware for the trailer connector and all the trailer lights before you connect it to the vehicle again. Lights will often be grounded through their mounting hardware, and if even one light has corrosion, build-up, or paint on the grounding area, this could be enough to cause a problem. Give the area a light sand if you do see any trouble spots.

I have included some links additional information and videos on wiring, including a standard trailer wiring diagram.

expert reply by: Sarah L