Lately the instrument panel has not been working, something seems to be loose. The speedometer works but the tach, fuel and temp gauges on the right side of the panel don’t work. Any ides as to why this may be?
The instrument cluster is really a single printed circuit board with lights and gauges stuck in it. It has a single connector into the wiring harness. After 24 years of heat, dust, moisture, vibration, things work loose, crack, become corroded, all that kind of stuff. Tearing down a dashboard is a job best left to those who do it for a living, and even then, positive results can be elusive…Good Luck.
Get a manual and see what’s involved with removing the instrument panel. On some cars it’s a complete pain in the butt, but on some cars it’s actually not too hard. Like Caddyman says, the electrical connector is the most likely culprit, but it could also be a broken plastic tab that’s preventing the panel from sitting in the right place or it could just be a plain old bad cluster. In the process of taking it apart, it should become fairly evident what the issue is.
Without a schematic handy, and seeing as how this is just about ancient history, I can only generalize.
It could be either a faulty connection on the back of the instrument cluster, a fuse block problem, or a faulty vibrator on the printed circuit.
This era of VW Rabbits were prone to some fuse block problems at times. You could try dropping the fuse block down and disconnecting/reconnecting each wire plug one at a time on the offchance a connector could be scaled over.
Dropping the fuse block is easy to do; drop the kick panel, one Phillips screw, and lower it down.
The fuel and temp gauges are controlled by a pronged voltage regulator (called a vibrator in slang) and failure of this vibrator or the power supply to it can cause the temp/fuel gauge to become inoperative. This should not affect the tachometer though. Checking this would require removal of the instrument cluster.
Not much to work with and realize it’s not too specific but that’s the best I can do off the top of my head. 
I’d be willing to hedge a bet with a poor connection on the back of the cluster. If that’s like every other '80s convertible Rabbit / Cabriolet, the top probably leaks a fair amount and the car is humid inside, promoting corrosion on connectors, particularly those that aren’t making very good contact to begin with.