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please add to FAQ: How to test Speedometer sending unit from in car.

posted by  someone claiming to be io333 on  Mon Mar 29 13:19 CST 2004 [RELATED]

This worked on a 1992 Volvo 740

Since no one could give me a difinitive answer as to whether this could be done, I just decided to go for it and see what happened.

I have a dead speedo and odomter. I couldn't figure out how to tell if it was the sender, the wiring to the speedo, or the speedo itself.

I have a 15 year old RadioShack analog VOM. I switched it to 10 volts alternating current range. I had a friend hold the leads on S+ and S- (those are the markings where the wires go into the speedometer. (The speedo was not in the car).

I drove up to approximately 15mph, and as I did, the needle smoothly moved up towards 1 volt. As I slowed down, the voltage dropped smoothly as well. As far as I can tell, this means that the pulse generator in the rear end is working fine, as is the wiring that comes from it. If I had known this beforehand, it would have saved me major headaches. Now I can just concentrate on getting the speedometer fixed.

Aside: does anyone know why the A/C compressor will not work when the instrument cluster is not in the dash? I hope I didn't fry anything in the A/C by trying to turn it on without the instruments in place.






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