The speedometer and odometer haven't worked since I got the truck. The odometer's stopped at 197,000. Ive replaced the tps sensor, the part that plugs into the other end. But what ive noticed is when the turn the key to the start position, and it only does it if the key has not been turned in a few hours, like overnight, but the speedometer needle will hop about a 1/2 inch, then go back down. All the other gauges work with the exception of the oil pressure guage witch will either be sitting dead or seemingly follow the rhythm of the rpms of me shifting through the gears. I really want the speedometer working again, what do I Need o do to fix it?

 

More than likely you have several bad connections between the VSS, speedo head, and PCM. The VSS is just a rotating switch that created an on/off pulse that increases with speed. Voltage for this pulse is supplied by the PCM.

 

I don't know if the pcm is good or not

 

Wiring issues can be a real pain. I've been fighting them on my 92 since I got it and I have a good electrical background. Here is a start: https://www.dieseltruckresource.com/...18&postcount=4 .
From there, It's pull connectors and grounds and check for corrosion.

 

After what Ive learned over the last few days, I believe the pcm is dead and things have been wired around it. Because my wait to start light has never came on, water in fuel light has never came on, speedometer has never worked, and im thinking the a/c wat hot wired before I got it. That sound like it could be the case?

 

I use an app on my phone called Ulysses Speedometer. Works great. ;-)