I had the same problem with my 87. It is probably in your harness, and not the gauges themselves. I had no gauges working, so I got the CSM (if you don't have one, get one....it is worth the money). I started tracing circuits, and found that I was getting power at the fusebox, but not at the gauges. I had no voltage at C1, which is on the connector for the cluster. I pulled the gauge cluster, and found that the harness had been wrapped in duct tape from the factory (not the first one I've seen like that). Check this link in another forum for more information:
http://www.gbodyolds.com/foru/showthread.php?t=369 Also, if you have the CSM, check for voltage at the C1 connector. If you do not, it is probably the problem I'm describing below. If you do, it may be a grounding issue like Anubis said.
I found that there was white corrosion from the tape. Looking at the schematic, there are several splices in the harness that connect the gauge cluster to the harness. It made sense that if it was getting power from the fusebox, but not at the gauges, the splice seemed the most likely area to look at. I pulled the dash, and went through the wiring. I replaced several of the splices, using some hollow copper connectors I bought at Home Depot. I found a trick on a Toyota site where they showed how to redo splices. Disclaimer: you may have to do a little experimenting to get the technique right, but this is the general way to do it...it's been nearly two years now, so I may be a bit fuzzy on the exact technique. If you are good at electrical repairs, this should be a breeze.
I cut the connector on one side, opened it up, put the wires in, crimped it down slightly, then soldered the wires in the connector. Crimped it down, and soldered it. Had a nice, clean and strong connection.
Retaped the harness with electrical tape, remounted it, and put it back in the dash. Hooked everything up, and tested it...had power to the gauges for the first time. The cluster can be a bit of a bear to put back in...you have to push the cluster into the connectors, and tighten the cluster down carefully.
I won't know whether the gauges will stay working until I actually drive the car. Hopefully, I got the screws tight enough to hold, and not allow the cluster to vibrate and loose connection.
Good luck!
