Isolating Brake Light Signal on 2008 Mercedes-Benz C350 for 3rd Brake Light

Question:

you recommended using 3rd Brake Light Logic Module on my 08 c350 but my signals are separate bulbs from my brake/ tail bulb. so why do i need this?

asked by: Michael P

Expert Reply:

It sounds like your 2008 Mercedes-Benz C350 uses Pulse Width Modulation, so you will need to use a converter compatible to capture the signal and convert it for use on your LED third brake light. For this I recommend using the Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector # C59236 and then you can use the Pacer Performance 3rd Brake Light Logic Module # PP20-702 after that converter to isolate the stop lamp from the turn signal.

expert reply by: Jason S

Michael

3/11/2019

you recommended using 3rd Brake Light Logic Module on my 08 c350 but my signals are separate bulbs from my brake/ tail bulb. so why do i need this?

Jason S.

3/11/2019

Vehicles are normally 3 wire or 2 wire systems. The three wire systems have separate running/tail lights, separate turn signals, and separate stop lamps. The two wire systems have separate running/tail lights and then combined turn/stop lamps on each side. You can use a circuit tester like # PTW2993 to probe the wires to determine function. It sounds like you either misunderstand the system you have as a three wire system, which then would not need the conversion isolator or if you have the combined turn and stop lamp signal why the converter is needed to isolate the stop lamp signal from the turn signal. Your 3rd brake light will have either two or three wires. A two wire light needs a stop lamp signal and a ground. A three wire system needs a stop lamp signal, a ground, and the third wire is either for cabin light or reverse light feature and will need to be wired for your preference for the white lights if integrated which is more common on a truck than a sedan.