craft1

I was talking with a friend today and we happen to be discussing the brake wear sensors on the MB vehicles and today he was asking me why the older models had 1 wire sensors and new models use 2 wire sensors. I know that in the older models and some newer models, the 1 wire sensor is used and when the pad reaches the limit, the wire in the sensor makes contact and the ground is complete to turn on the warning light. basically the sensor sends a ground signal to complete the circuit. Now I know they were having problem with this because aftermarket and independent shops would do brake jobs and not install sensors and basically the light wouldnt ever come on when pads were needed again so MB came up with the idea for the 2 wire sensor. But I forgot how the 2 wire sensor operated. I know that if the sensor is left off the vehicle, the light will stay on untill the sensor is installed. But how does the circuit operate for the 2 wire sensor?

Does anyone know how this works so I can explain it to my friend.