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Trouble Locating Cold Side of Stop Light Switch for Brake Controller on 2014 Mercedes-Benz Sprinter


Hey there, I bought the universal kit for trailer brake controller -7 way item # ETBC7 for 2500 Sprinter 2014 year. Had it all installed the way it shows on the video. Everything went nice till I got to the very last part - connecting the red wire from the brake controller to the cold side of the brake switch. So next step is to check which wire will get hot wire tester red light turns on when you press the brake pedal. So here is the problem: I got the brake switch which is located on top of the brake pedal like on every 2014 sprinter. Mine has 5 wires: 2 browns, 1 yellow, 1 red with white stripe and 1 brown with red stripe. I have tested all the wires, none of them would be cold and become hot when the brake pedal is pressed. Even more than that I got the yellow wire and the red with white stripe which are hot all the time solid strong light on the tester no matter if you press or not the brake pedal. One of the brown wires and the brown with the red stripe are also hot all the time no matter if you press the pedal or not solid but the light is not as strong as on the yellow and red w/white stripe and the last wire brown is cold all the time, no matter if you push the brake pedal or not. What should I do, to which wire should I connect the red wire of the brake controller? Thank you


Expert Reply:

There are some wires that are hot all of the time which is why we usually try to emphasize that the brake controller, like the Prodigy P3 # 90195, needs to be connected to the cold side of the stop light switch when installing the Kit # ETBC7.

Sometimes a vehicle will not have a wire connected to the cold side of the stop light switch which is what you are finding. In that case you will simply need to install the Roadmaster Stop Light Switch Kit # RM-751475. This is typically used for flat towing applications but we have found that when installing a brake controller in a Mercedes-Benz Sprinter, like what you have, you may need to install this kit.

You will just need to run the red wire from your brake controller to this kit for the brake controller to function properly.

Installation instructions have been linked for you to check out.

click to enlarge
expert reply by:
Jon G

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