I recently purchased a second-hand ML320 towbar to fit to my 2009 ML.

I came complete with the trailer controller (MCLASS TRALER MCU)


Trailer Controller

I have these connections:



Connections on Trailer Controller

Closeup of connections on trailer controller

I'm guessing the RED wire with the in-line goes to a source of power from the rear fusebox.

Confused about the white wire and the two small connectors.

Also wondeing how to connect my brake controller.

I have read another trailer wiring forum here, but it kept referring to green connectors etc.

How do I get this to work?

Guessing I may also need a new rear SAM? If so, what model?



My Rear SAM (2009 - ML320)


Any help would be appreciated.

 

Are you sure you got the correct hitch and harness? It does not look like you do. The harness should have a plug that plugs into the rear SAM, a ground wire, and 1 or 2 fuses that plug into the fusebox. You have the correct SAM, but it will need to be programmed along with the central gateway.

 

That is an aftermarket trailer wiring setup

 

it is indeed and that is unauthorized use of Mercedes trademark. Not a Mercedes part number.

what you require is original Mercedes harness that connects to your rear SAM (signal acquisition module)

I know GL better than ML but think they are the same … there should already be an unused green connector hanging under dash on driver side to which you connect your controller. This wiring leads to the rear SAM. You purchase other gender green connector block and pins from Mercedes to fabricate or modify wiring from there to your controller.

I have two early 2007 (first year) GL that did not get the factory harness to driver area factory installed. I installed this purchasing the factory harness and removing/reinstalling a lot of the interiors. The diesel had hitch retrofitted by dealer and required a replacement rear SAM. Green connector on SAM matched the new controller harness. The 450 had factory installed hitch, but had to change the gender of the controller harness connector to mate to the SAM.

with trailer connected via Mercedes SAM, you get bulb monitoring and if you have GL you get signal to not lower vehicle (Airmatic) at highway speed as occurs otherwise. You will have a little more work to do if your trailer has led lighting.

 

That is very interesting. I'll have to see if the same is true on my ML350 bluetec; seems like a modified trailer plug would be an easy way to trick the car into staying high when wanted if that is the case.

 

Hi R0Bs. Did you ever resolve this? I am asking because i bought an '06 ML320 CDI with a tow bar, but it turns out the electrics aren't working because that little box (PB420) is missing.
For what it's worth, that box was commissioned by Mercedes Australia, and made by Lumen Pty Ltd. So it's not entirely aftermarket, nor was it incorrect use of the Mercedes logo...

Keen to learn what you did to solve your towing electrics issue.

Cheers,
PJ