Your dimmer switch problem is a common one, the springs in the rheostat go bad after a while. The fix for this is either to completely replace the rheostat, or solder in a jumper wire in between the two solder joints in the dash. It will be on max bright all the time but as you noted, it isn't all that bright.

I'd guess that the clock is unrelated to the rheostat. If you take a look at the back of the dash, there are a number of plugs, a few of which supply power. There are several clock repair DIYs floating around that should help you. For this and the rheo, you'll have to pull the cluster out with a couple of handy coathangers.

Your fuel gauge is most likely again unrelated. I have the same problem on my 126, and it is probably caused by an algae growth inside the fuel tank. Those little things love diesel fuel and will grow if you leave it for a while. The sending unit will need to be cleaned if a bottle of biobor doesn't work over the course of a few tanks of fuel.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth