I have a 1993 chev silverado. I have owned it for five years, The problem I have is the speedo bounces all over when driving. I've changed the sensor and the control box behind the glove box, and still the same. It once had a remote starter in it which was taken out, and I've always wondered if that had something to do with it. Any help or ideas would be great!

 

sounds like you need a new guage cluster

 

Thanks, I should of included that I've done that.

 

better check the wiring

 

The VSS (vehicle speed sensor) works by generating AC current. Your alternator generates AC current and diodes converts it to DC current. If the diodes in the alternator go bad and let AC current leak into the trucks electrical system messing with anything that uses AC current like the VSS. You need to have your alternator tested at a shop that has the proper equipment to do it. It should not cost very much to test at my shop a electrical system test (battery,starter and alternator) is only $19.99

 

Thanks so much for the info. I will certainly do that. I think the alt has been replaced once since I've had the truck, but I will have to look back at my records. I have tried just about everything so I will sure get the alt tested. Thanks again, I will keep you informed.

 

If all else fails, a GPS will show your speed much more accurately than any other speedometer. They're going pretty cheap nowadays too.