|Variable Speed Sensor_______________________________|
The speedometer is driven by the variable speed sensor (VSS), which is currently available only from OPMD (www.opmd.com).
One way is to use a speedo with a drill and 12 volts.
It looks like it won't be easily repaired, except for something like a broken wire.
Above, there are two different styles of sensors shown (thanks to Jeff Herson at Merkur Parts Midwest www.MERKURMIDWEST.com for the donor). The plug that fits into the body holds a circuit board with (probably) a transistor that pulses when the vanes of the rotor pass between it and a magnet held in the body of the sensor. Transistor shown at about 10 o'clock on the circuit board.
The transistor is shown at about 9 o'clock on the circuit board. The magnet is visible at about 6 o'clock behind the vanes in the body.
As much as I had to cut this one to open it, it would still probably be usable, if it were repairable. That I leave to the electronics experts. See next picture:
This is the top of the circuit board, with several other components.