Speedo worked when I parked the truck for a few months. Put a new battery in it finally and I'm pretty sure it worked right after I put the new battery in but the next day it wasn't working and hasn't worked since. Is the speed sensor on top of the rear diff? Or is it on the transmission?

 

I'm guessing you have a 97? If so, you have an analog cluster, not a digital mileage readout cluster.

There is a VSS at the tail end of the transmission. It has wires going to it so you can't miss it. If it is bad the speedo won't work and the transmission won't shift right. The 97-98's have a gear mesh problem when they get high mileage. The quit working. If you find it is that, they make a kit (I don't remember who sells it, but its out there) to repair the gears. It's either that or find another cluster to install. Good luck.

 

Yeah it's a 98, I haven't had time to crawl under it to see if it had the gear in the transmission or was an electric sensor on the rear

 

I believe the worm gear is for the Odo only. The speedo should still work if it was a gear problem. I had trouble with intermittents on Oil, Battery, and a tach that was off by 700 RPM. You can get pristine replacement clusters off Craigslist, Ebay or a local salvage yard (I got mine for $60, and a cheaper one was posted a week later). Everything worked (we don't have PATS like the '99+ models do, so it was a hassle-free swap - even put in new LEDs at the same time).