Bypassed rheostat...worked for a bit then smoke and blown fuse
 

The dash lights are out (just the lights on top that illuminate the gauges), so I replaced the bulbs and fuses but still a no go. Figuring it must be a fried rheostat (which it was) I took it out and soldered a jumper wire between the contacts. Dash lights came back for a brief couple minutes, but not before smoke came out of the dash and the #1 fuse (white/square) was blown. Tried another white fuse, then a red...dash lights aren't coming back. My ghetto rigged rheostat seems ok...tell me I didn't somehow fry the circuits in the dash?

hmm..

did you take the whole rheostat out? (stupid question, i know) other than that you may have shorted one of the pins from the rheostat to ground, in that case you'd have that kind of current to make smoke and blow fuses.

check all the new bulbs to make sure the contacts aren't shorting out, you definitely have a short in there somewhere.

After you have followed Nick's advice, try taking out all of the bulbs . . . every one, including the ones you didn't know about until you looked for the third time. Then put in a new white fuse and power up the car. If the fuse still blows, you have a short somewhere, perhaps something associated with the rheostat jumpering or perhaps a wire is touching something it shouldn't.

If the fuse doesn't blow, then something changed when you removed the bulbs. Put the bulbs back in, one at a time, and see what happens. If one bulb causes the fuse to blow, the problem is there.

If you get all the bulbs back in and they all work and the fuse doesn't blow, then you have un-disturbed whatever caused the problem in the first place. Be happy and hope it doesn't return.

Jeremy

Everything else in the dash works, including the warning buzzer which is on the same fuse. I think the problem may have been the exposed (stupid, I know) jumper wire touching something. I replaced it with a shielded wire but still no dash illumination. I'm borrowing a multimeter today to test out the dash bulb sockets. Hopefully I just blew the bulbs and there's nothing wrong with the circuitry. In the mean time I will try what you said about removing the other bulbs. My radio circuitry problems were resolved a similar way: I couldn't pick up any stations until I opened the ash tray and pressed the cigarette lighter in. Old funky electronics.

while you are there, look for any obvious hot marks on the back of the dash.

How much smoke?

With the proper fuse installed the chances of melting wires is nil.
I don't recall if the back of the w123 speedo has a pcb with this circuit routed thru a trace. Look there for signs of damage.

Find and fix your short then you can solder a wire across the damaged (melted) trace.