I've recently encountered (2) un-related problems. First my rear left window motor would roll down, but not up. I've tried 2 good motors from a donor car, all with the same results. I've also swapped good switches and still the same problems. Second problem happened while installing a tachometer in place of the clock, now my odometer and trip odemeter doesn,t work. I disconnected the battery before I started.I've checked the connections and everything seems to be fine. Also the instrument panel doesn't light up, checked the rheostat seems to be good. Could I have shorted something? is there anything else to check. All the other instruments still work(speedometer, new tach,gas and temp gauges). Any suggestions will be greatly appreciated.
thanks in advance.

I would guess a broken wire in one of the door hinges for the window. Either in the drivers door hinge or the door with the window thats not working. The left doors get used the most so the wires tend to break. If you pull the rubber bellows out of the door pillar you can see the wires in the hinge and the break is usually obvious.
As for your instrument cluster. Have you checked the bulbs in the instrument panel. I know it sounds strange but they often burn out when you work on the cluster. I have had the happen quite a few times.
I'm not sure about the spedometer/odometer. I'd check the wire connection. It does not stay in that well after the anti-tamper clip is broken off. There is also a gear that goes bad in the spedos, and the symptom is no odometer.