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My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
On some models the Rear sam needs replaced in order to install this trailer brake harness to fit the harness.Remove the passenger rear panel where the rear fuse panel is located and see if you locate a green wiring connector hanging or taped into a harness next to the fuse panel.If you do let me know as I show a procedure on how to connect a trailer brake.If you do not let me know as the sam may need replaced and harness ordered.
If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete.
On this model it would have to usually be pre wired for brake controller and the harness for this brake controller is found in the rear passenger side near the rear fuse panel with a green connector usually hanging loose or taped to a harness near the fuse panel.This is the brake control harness that is used.Does your model have this connector at all?
Let me know,thanks Pete
Are you talking about the brake switch plug,the switch that activates the brake lights?
The only connection I know of for the brake controller is at the rear by the rear interior fuse paneling.Usually the wiring at the brake switch or connector under dash is a data signal wire on Mercedes that won't work for wiring a brake controller as it isn't a signal wire.The connection at the rear (if equipped) is the one needed for the brake signal.
If your model does not have this connection let me know or if you would prefer for someone else to try and help here let me know.
I don't know of a connector under dash that will work on this model here myself.My info shows a green connector at the rear fuse panel that needs tied into to activate the brake controller when brakes are applied.Is there any way you can snap a picture of this connector you have located and upload it here?