Originally Posted by VW1300

FWIW, this is what happened to me last year - my '85 tach was working only sometimes. My OVP was new and I replaced the sensor on the flywheel.

It so happened that I took the car in for A/C service - wasn't working at all. Mechanic found something amiss under the hood, said it was part of the electronics - and the A/C was working again. Lo and behold so was the tach. If I had known that was going to happen, I would have asked more questions on what he did. But if your A/C isn't working, it could be related.?.