wheeljo2

I have a 2009 GL550 with tow package. I purchased a 7 to 4 pin adapter to connect to my boat trailer and no lights. I checked all same 7 pins on my factory plug in adapter and only had one hot lead on my test light. Is there a button or other programming I need to do to get the wiring harness to fire up my tail/brake/turn signals?

Thanks for your help

itb76

Yes the vehicle needs to be programmed for a trailer, but if it came with the towing package from the factory it should already be activated.

sdslm11

Did you figured out what was wrong, or if you took it to dealer what they did? I have the same problem and i found it at the last moment and the whole long weekend trip went down in water as i didnt had any lights on my trailer. If you can keep me updated that would be awesome. THanks

henryng

I got the same problem and it needed to have the dealer reprogram the SAM.

not2fast

Mine stopped working. I wonder if there is a fuse for it. I will have to hunt that down.

not2fast

Fuse listing

http://www.mercedesmedic.com/gl-fuse-chart-x164/