Unable to turn rear wiper off
 

Bought a replacement rear wiper motor (old motor had siezed internally) from ebay which was all good for 3 months then as I drove one day the rear wiper came on by itself and I was unable to switch it off and I was in fast moving traffic so unable to pull over to switch ignition off.
Rear wiper eventually stopped after 4 or 5 mins so presumably I start at the fuse, or is there a relay in circuit then will be looking at the motor and wires.
Any other advice much appreciated, cheers

I'd start at the motor.

Remove the permanent 12 volt supply from the connector when the wiper is 'doing it's own thing', if the wiper stops it's the park switch that's faulty.

If it is the switch you could try swapping the one from your old seized motor if you still have it. Most wiper motors/switch assemblies are complete units but you can usually manage to swap out the switch.

Small consolation now, but the motors are very easy to strip, de-grunge, and reassemble. We had one on the bench for a chap at work not long before I retired, required only a torx driver to dismantle.