[RivermasterNC]

My recommendation would be to replace the speedo and odometer with an electronic one. On a budget, look for a used one at a salvage yard.

If you find one that the odometer does not seem to work, fear not. It is probably a problem with a slipping pot metal gear on the odometer drum shaft.

Speedometer accuracy will be dependant on wheel diameter and rear end differential ratios also.

 

[RivermasterNC]

My wiring diagram shows a direct conductor (wire) from the #1 connecting pin at the transmission to the #5 connecting pin on the back of the instrument cluster containing the speedometer. The conductor is a 0.75 mm diameter wire (white).