My 88 has a weird issue. The speedometer hasn't worked since I bought it. First noticed the plastic connecting the speedometer was broke so I ordered a new cable. Replaced the cable, nothing. I did notice that the cable itself was working when the speedometer wasn't hooked up. I went ahead and pulled another speedometer and replaced it. Still nothing. Then when driving I was trying to make sure everything was hooked up and pulled the gauge cluster out a bit and the speedometer started working. Placed it back in place and no go. Pull it out again and speedometer worked. Any ideas? I am thinking some kind of a ground issue even though the speedometer is mechanical? All other gauges function properly (actual guages not dummy lights). I've done all the grounding recommended by cruiser including the dash grounding. Any ideas would be greatly appreciated. Oh and it does have cruise although it doesn't work and wouldn't work without the speedometer anyways, I think. This is the last obstacle I've got preventing me from passing inspection here in Texas.

 

If you have cruise, I believe you have a 2-piece cable with a cruise transducer in between, somewhere behind the cluster. Follow the cable from the speedometer and you'll find it.
Seems like it works when you jockey it just right, I'd poke around that transducer and see what's loose or not fitting right. .