Hi Art, Thanks for the reply.

The term D'arsoval Movement is etched in my memory but I don't recall ever understanding what it meant. It's simple enough and explains the M in your hand made drawing of the circuit board. It's beyond my capability to fully understand that drawing but my guess is that the signal from the speed sensor is shared by both the motor and the meter to regulate them.

I'm slow to respond because I wasn't sure if the odo was failing with the speedo. I seem to remember that it was, but the unit has been in the car for over 4K and I've gotten into the habit of smacking the dash when the needle gets my attention. Looking at the odo takes a conscious effort. We had a 200 mile return trip to Montreal planned for last weekend so I thought I'd verify it then.

About half the time the needle will hit 0 and rebound instantaneously to speed. 30 miles in, it had done that twice, but at 50 miles it hit zero and stuck. And, yes, the odo stopped as well. So I tapped the dash as usual and nothing. Shutting down the car at home 150 miles later, there's been no more activity on either odo or speedo, so it looks like the fault is holding. Curiously, it's sitting at precisely 198 k.

I'd like to power it up on the bench and probe around but I'm not sure if I can do that. I have a spare L connector and the 90 wiring diagram I have shows the speed sensor wires, replaced by the AC adaptor I think, connected to the black and the green/white. If I powered it with a battery or battery charger, the positive would go to blue, but I' not sure about the negative and I'd rather not blow it up.

It worked remotely before with only 3 wires, so if I had to guess I'd say the black is ground for both the sensor and the 12V.

Perhaps there's a better approach than this, and I'm open to any.

regards, Peter