Go to http://cleanflametrap.com

Lower down Art has notes on the electronic speedo and replacing the odo gear.

If you look at the 10th pic of the odo repair and compare it to the wiring in the electronic speedo notes, you'll see a neat way to bench test the speedo. But you'll need a low voltage transformer that puts out an AC current. The A/C provides the pulse to mimic the impulse sender.

With the cluster together, attach +ve 12v to the upper tab, -ve 12V to the center tab, and the A/C output to the lower and center tab. The speedo and odo should work.
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1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.