Canbus decoders can be found from quite a few dealers on the net. The adaptor wil allow you to decode the can signal and get the following dependant on interface:
Ignition sense,
Reverse,
Dimmer / illumination,
Speed pulse
Steering wheel controls
There are some basic canbus convertors that will just give you speed pulse.
As far as I am aware, most ABS systems are still analogue, so as Craig says goto the ABS pump or control module.
You will find the AVIC units will run without the speed pulse wire not connected, the nav is just sometimes a little jerky as its trying to just use GPS and gyro
Andy