Classic/Antique Car Repair: Speed Odometer on 1980 Rolls, speedometer cable, female connector

Question
I have a 1980 Silver Shadow II an the speed odometer doesn't work. I have replaced the sensor on the transmission but still no luck. I have started checking voltage and I only show a small amount, .4 volts, at the sensor which is the wire coming from the speed odometer. Trying to figure out if that should be battery voltage or something like a reference voltage. Seems that less than a 1/2 volt is to little and might be my problem. I have a wiring diagram but not a lot of information on what voltage should be where. If you have any information I would appreciate it.

Answer
If the odometer works, but he speedometer doesn't,
your problem is most like in the cable or the female
connection threads has worn. You will have to pull the
speedometer cable to see if the problem is the cable or unit female
connector is broken. You may need to have it rebuilt as in did 5 years ago.