Converting to electronic speedo

It depends on the speedo itself (it's PPM), your rear axle ratio and the diameter of your tires. Maybe some other things too.
The PPM is the number of electrical pulses it needs to register one mile on the odometer. If you get the odometer working accurately, the speedo will also be accurate.
If the paperwork that came with your speedo doesn't say what you need, you might need to visit a local speedometer shop and get their advice.

If your speedometer requires 8,000 pulses, you can get an 8K pulse generator from Dakota Digital. The part number is SEN-01-CHR. That would be pretty simple.

It can get pretty complicated, so I recommend a speedo shop if you aren't able to figure it out. You might need to change out the gear in the transmission.

Another option is to get most any VSS (Vehicle Speed Sensor) that will work with your transmission and use an external adapter to convert the signal to the correct PPM for your speedometer.

The only reason I know any of this is because the mechanical VSS adapter on my 92 Ram pickup has stripped/worn out gears. They haven't been available from Dodge for years, so getting my speedo working again is requiring a lot of research and learning.:read2: It's pretty interesting, but I sure wish I could just buy a new adapter at the dealer and be done with it...