I recently drove my electronic speedo on the bench. 1982 300sd is electronic and required a signal generator and 12v power supply.
Details here
Fixed 1982 300SD odometer slip at high speed
Getting it up and running on the bench was priceless for troubleshooting. My problem was in the stepper motor portion of the speedometer (that is the odometer I guess).
a drill won't work on this style of odometer.