Trailer Running Lights Do Not Work When Connected to 2014 Mercedes ML 350 BlueTec

Question:

Hi, I have a Prodigy RF brake system installed on my Mercedes 350 ML Bluetec. I used the adapter 20142 with Lamp out sensor bypass to pair the brakes. All parts purchased from ETrailer. The pairing of the brakes worked perfectly. However, I cannot get the tail/running lights to work. They flash intermittently but will not light up when the lights are activated. The brake lights and turn signal lights work fine. I have checked the pins and they seem to be aligned properly. Any suggestions on what I can to do get the running lights to work?

asked by: Ross P

Expert Reply:

It sounds like there is either a ground problem on the trailer or adapter # 20142 is not offering enough resistance to power the lights properly.

Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the grounds are all fine then the likely cause is not enough resistance from the lights. You would only need to install one load resistor on the running light circuit (or two if the running light circuit is split at the trailer connector) to solve this problem. For a pair use # DI34ZR.

expert reply by: Michael H