I am having the exact same problem with the instrument panel not working, or the fan not engaging. Everything else electrical on the vehicle works. I also have a 1994 Ford Mustang GT convertible. I have replaced the Instrument cluster with another one. Gauges still not work, all I can get is the lights to light up behind cluster And the right signal works. As with the fan I turn on the AC, the fan should turn on but it is a no go. If you have any information on how to troubleshoot or fix this it would be appreciated thanks.
I assume a couple of things right off the back. Once upon a time i heard this is usually a problem with the wiring in the instrument cluster and just requires some love.
However, if you want to check if it is the gear, it is very easy to pull the cluster out and open it. You will be able to see clearly if the gear is broken in the back of the cluster and it us a cheap part to fix.
I am not exactly a mechanic but have needed to pull my cluster to change the gears in my ODO, not not at all hard or time consuming.
Have you figured it out yet? If you say what you did you could really help out a Google warrior down the road
Also, idk if it will throw codes for it not working but I assume it would, you can use this technique to dump your codes with the EEC, maybe you will find something good. It only takes a paper clip/wire, pen and paper, and 5 minutes of your time. Best part is you can save 20-30$ on not getting an OBD1