Anyone know how ABS systems work? I mean are they electrical or mechanical? what actually controls them?

this is just ideal speculation but you know what they say.... knowledge is...erm...something something.

ABS as I know it consists of a bunch of sensors (typically 1 per wheel) which are connected to a controller. Using these sensors the controller can detect when a wheel is locked and then modulate the braking on that wheel. The bit that does that hard work is basically just a pump and a bunch of valves allowing the braking to each wheel to be modulated invidually.

ABS systems are controlled by computer. There are two electronically operated valves per channel (usually one channel per wheel). One valve isolates the wheel from the brake pedal to stop you adding more pressure, the other dumps the pressure already in the wheel to a reservoir. A pump pumps the excess fluid back into the master cylinder to stop the brake pedal traveling to the floor.

There is a wheel speed sensor in each channel. The computer monitors the speeds of each wheel constantly. if, during braking, it sees one or more wheels slowing down more than it should it releases some of the brake pressure in that wheel and re-applies it slowly. if the wheel starts to lock up again then it releases some pressure again.

modern ABS systems will find the maximum brake force for each wheel and keep them there. they call it electronic brake force distribution.