1994 GMC Truck V8 Four Wheel Drive Manual 158000 miles
My speedometer started jumping up and down.
It would read correctly at 60 mph and then start jumping between 20 and 45 mph then it would read fine. How do I know if it is my vehicle speed sensor or my speedometer? Could it be something else?
It could be your speed sensor, you can check the ohms to see if it's grounding out or having to high of ohms. Or it could be the speedo or the wiring or connections are in poor shape. I'd start at teh bottom as that is more in the weather than the speedo head.