Trailer Lights Won't Work on 2011 Mercedes-Benz GL on Trailer With 4-Way

Question:

Hello, my GL550 towing connection with the adapter will power up UHAUL trailer lights , BUT brakes and turn signals will not function. UHAUL tested the power from auto and the adapter and says it’s fine. Same problem though, running lights work, but not the brakes or turn signals! Thank you

asked by: Rolanzo K

Expert Reply:

I'm not sure why U-haul would say it's fine when it clearly isn't, but the problem with the Mercedes is that there isn't enough power draw, so you'd need to use a lamp-out adapter:

- 7-Way to 4-Way/5-Way Trailer Adapter for Vehicles with Lamp-Out Sensors # C35FR

This will allow the trailer's brake and turn signals to recognize the signals coming from your Mercedes. If you were already using one of these adapters (I wasn't sure if you were talking about one of those or a 4-way to 7-way like # C57672), then U-Haul would need to install load resistors in the trailer for it to work.

expert reply by: Kyle S