Well my ABS light was on (previous owner disconnected the loom I think) so I ran a VAG-COM scan - front left ABS sensor, resistance too high.
Went to check it out and noticed this:

So, I think it's safe to say that's something to do with the problem

I tested the resistance across the sensor at 1.03k Ohms so I believe that is correct.
Chasing the wiring back into the engine bay reveals a plethora of insulation tape and crimped connectors (starting to think this car might be a bit of a turkey), so I want to check the wiring is ok before I go replacing the sensor.
Question: Does the ABS system constantly send a current through the wiring when the ignition is on (allowing me to check current is getting down to the connector)? Or could I continuity test the +ve and -ve parts of the wire at various points along it (back towards the engine bay)?
At the moment the right rear locks up under heavy braking, sending the car sideways... so any help is appreciated!
Adam