what is your skill set, when it comes to working on cars? The aforementioned abs sensor system is one of the simpilest things on the car. On each wheel, with the wheel removed, you will see a ring that looks like a toothed gear. near it will be the sensor itself, which is nothing more than a electromagnet. As the "teeth" of the sensor ring pass by the sensor (magnet) it creats a electric pulse. If there is too much rust on the teeth of this ring, it could affect the ability of the sensor. So the easiest and free thing you can do is remove the front wheels and wire brush off any rust build up. See if that takes care of the light.

As for your brake pads almost wearing down to the point of scoring your rotors, that meant either your previous set of brake pads did not have the wear sensors in place, or and less likely, the brake wear bulb in your dash is burnt out. The sensors again are really realy simple. Simply put it is nothing more than a that sits in a slot in the pad. When the pad thickness gets down to about 2mm, the wire would then be touching the rotor, completing an electric circuit, which illuminates the brake wear light on your dash.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member