After bringing my 97 1.8tQ to the garage to get the wheel bearings done my abs light and brake light are constantly on. Brought it back to them and they determined it to be the left rear abs sensor. Claiming that it must of been a quincadence because their work did not cause the sensor to go bad. So im pretty sure i can get a used one and install with a little direction. Tried searching how to install but came up empty. Thanks

 

Hmm, this one might help?
http://www.audiworld.com/tech/elec116.shtml

If not, there's a great Audi DIY site here.
http://www.audidiy.com/b5a4.html

 

They have to work right around the sensor to do the bearings. Chances are they a) damaged it removing it or working on the bearing, or b) unplugged it from under the seat so they could leave it in the hub when they changed the bearing, and didn't reconnect it. It sucks that they won't own up to the possibility of damage, but it's also possible that it just decided to fail. Take a look at it and see if it looks mangled in any way - they're a bastard to get out of the hub unless you have the hub off and are tapping them out from the inside of the hub.