I've had a problem for a while with my speedometer where it would do strange things. Initially the problem started where the speedometer needle would sometimes hang up and then jump to the current speed. Eventually it got to where sometimes it would be totally dead (0mph at any speed), or it would spin all the way around the dial and peg out against the bottom of the 0mph peg, or it would wander around between the 3 and 8 o'clock positions on the dial. Tapping the panel would sometimes make it start working normally or make it enter one of the other wierd mods of operation and it was also affected by changes in ambient temps. The odometer never had any problems. Anyway, I disassembled the speedometer cluster and found several broken solder joints where the 4 pins that go to the speedometer's meter movement connect to the board with the IC that converts the incoming pulse stream to a voltage for the speedometer. Cleaned up the contacts and resoldered the contact pads and its been working fine ever since.
Separated the white and the black parts of the cluster:
Unscrewed the speedometer gauge (look at the tutorial above to see which screws).
Popped off the Speedo PCB:
Then I proceeded to reflow some of the joints. To do this, I just touched the tip of the iron on the join and held it till the joint got liquidy. I also fed in some thin solder I had, you might not need to, I just did it cause I had it lying around.
You can see in the pics some of the ones I touched up. If you look at the speedo, you can see 4 pins in a row (2 and 2), I focused on the points where they pin into on the PCB.
I'm pretty sure it is these 4:
If you're pretty good with it, touch up anyones that you can. I did, so I'm not sure if touching just those 4 would fix it. Any ones that were reachable, I did. Didn't touch any that had glue around them.