Tapping Into Reverse Light Circuit on 2015 Mercedes GLK for Electric Reverse Lockout Solenoid

Question:

I had a standard 2inch square hitch installed. But the GLK will not turn on the switch to lock out the brakes in reverse. According to Mercedes dealor, they will NOT sell me the part that allows the switch to engage and it only comes with their $900 hitch PLUS installation. There MUST be a way around this as this is nuts.

asked by: Ronald M

Expert Reply:

My first question is what type of connector is on your 2015 Mercedes GLK? If it is a 7-Way blade style connector then the center pin should be the reverse light circuit. The matching 7-Way on the trailer side would need to have an electric reverse lockout solenoid that is wired to the center pin.

If you have a 5-Way flat connector on the trailer and only a 4-Way flat on the vehicle then you would need an adapter such as # 20036. The extra blue wire would have to be spliced into one of the vehicle's reverse light wires.

I do believe the reverse lights on the 2015 GLK are on the sides of the vehicle and not in the rear hatch door, which is a good thing. You should be able to tap into a reverse light wire by removing one of the tail light housings for the vehicle to gain access to the wiring to it. Then you would use the included quick splice connector to tap into the vehicle reverse light wire.

It is possible that the extra draw of a reverse lockout solenoid will cause an error code to put up on the dash of the vehicle when you are in reverse. The only way around that is to have the factory harness installed.

Another option is to install free-backing brakes on the trailer. This will allow you to back up the trailer without the brakes engaging. I would need to know the size brakes you have now and the mounting hole pattern they have to determine if we have free-backing brakes that will fit. For the size of the brakes you can measure the width and inner diameter of the drum like in the picture I have included.

If you have a different connector let me know what it is and if it is factory or aftermarket and I can make additional recommendations.