Brake pads

[Lightning]

The pad sensor is just a loop of wire that the ECU puts a small amount of current through. When you've worn enough of the pad, you then wear through the pad sensor, breaking the connection, which the ECU sees as a low pad.

If you're going to use track-oriented pads without wear sensor holes in them, save your old broken wear sensors. All you have to do is cut the wires on the old pad sensor a few inches below the connector (at the strut), twist them together, and either solder or crimp splice them together to re-establish the connectivity and get the light to turn off. Remember you will then need to use the two wear sensors in your head to avoid rotor damage...