Brake Controller Installation in 2015 Mercedes ML 350 4Matic with Factory Tow Package

Question:

I am confused: The brake controller you list for my vehicle says it will work by simply plugging into the 7-way connector on my vehicle. However there is also a 4 pin box not flat connector under the dash, which is according to Mercedes a brake controller connection. I would like to use the Tekonsha P3 controller as the RF has a lot of features I will never use we only tow with one vehicle etc. Will the P3 work? Is there a vehicle specific wiring adapter so I can plug and playinch and if so, what is the part number? Thanks!

asked by: Robert D

Expert Reply:

There is no Tekonsha brake controller wiring adapter made for your 2015 Mercedes-Benz M-Class with factory tow package so your best options for a brake controller are the wireless Curt Echo # C51180 or you can do a wired installation of the Prodigy P3 # 90195 if you can confirm that you have the needed signals on each of the wires leading to the under-dash connector.

The P3 requires four connections for installation: ground (white), +12V power (black), brake light switch signal (red) and brake signal output to the 7-way (blue wire). If you have a circuit tester like # PTW2993 you can test the pins on the OEM connector to determine if it has the needed signals. Wire colors may differ from those on the controller (noted above) so testing is the best way to know you have found the correct wire for each connection to the controller.

When you test you should find one wire with +12V all the time (this goes to the P3's black power wire). Another wire should carry a signal ONLY when you press the brake pedal (this goes to the red wire). The other two pins will be ground and output to the 7-way. These connect to the white and blue wires, respectively, on the controller.

If Mercedes happens to offer a wiring harness for their brake controller port, then you could obtain that from the dealer and splice it to the pigtail leads included in the P3. If not then you will need to access those wires upstream of the connector.

expert reply by: Adam R