Troubleshooting Flashing Trailer Lights with 2013 BMW 5 Series

Updated 12/26/2014 | Published 12/25/2014

Products Featured in This Question

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(125)

$62.06

Hook Probe Circuit Tester

(60)

$13.72

Question:

Just installed a converter in my Mercedes c320 Automatic. I have a mission 6x12 mission trailer. When I turn the lights on the car lights on the trailer light up for a few seconds and then fade out. When I press the brake pedal, all the lights on the trailer light up. With the brakes pushed the right and left blinkers work. When i take my foot off the brakes within a second or two the lights go off. Thanks in advance for any help you can provide

asked by: Chris

Expert Reply:

The first thing I recommend you do is disconnect your trailer. Then you will need a circuit tester, like # PTW2993, to test the wires leading into the converter box for your T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector, # 118349. Next run through all the functions of the vehicle (left/right turn signals, brake lights, and running lights) while testing the wires.

If the signals are not correct going in there that indicates a problem with the vehicle wiring that will need to be addressed.

If the signals are correct going in, the next step is to test the wires coming out of the converter. If the signals are not correct coming out then there is a problem inside the converter and the converter will need to be replaced. If the signals are correct then the issue is on the trailer and not the vehicle.

On the trailer side, the problem could be one of two things. It could either be a ground problem or the lights on the trailer draw more power than the converter is rated for (4 amps stop/turn and 4 amp tail lights). For the grounds you will want to check the main trailer connector ground, the grounds for all of the lights, and even make sure the converter box on the vehicle are all grounded to clean and corrosion free bare metal surfaces.

To determine if the trailer is drawing too much power you will need to look at the light draw of each running light. The ratings should be on the light housings. If the total is greater than 4 amps then you know you are pulling too much power. Switching to LEDs would be the way to go for this problem.

expert reply by: Chris O