A couple of questions:
1. I checked the output that feeds from the course computer to the autopilot motor
and it shows +/- 7 volts. Is that normal? I'd have though it should go +/- 12v? It is a ST50 Autohelm
system from 1996 but upgraded in 2003.
2. I removed the old faulty chain drive unit (which is receiving the +/- 7v) and it is really small like this below. It is actually a windscreen wiper motor
and found it for sale in Germany here
. It only outputs 2nm and rated at 12v.
Note. I can't say what it was like before as it stopped working only a few hours after I bought the boat.