Bought that little voltage regulator 2 years ago for $35 for an '80 240 which provides lower than 12 volts for the fuel/temp gauges. Some dealers will give you a 10% discount for vehicles with 100k+ miles on some items if you mention it.

/// The instrument voltage regulator for your car is plugged on the back of the gas/temp gauge. It has three spaced fast-on terminals so it can't be put back on wrong. Bad news-- the last one I bought was $30 years ago. Hold your hand over the fuse block after running the car and clean any that ore hot. Check your ignition switch if there are problems with the wipers, radio, etc. You can unplug the switch and stick correct sized soid copper wire into the holes to hot wire and check the ignition switch.

The power windows were dealer installed in the 4 cylinder car, most likely. Is there a plug in the door panel where the window crank would have been? The 6 cylinder cars had 4 power windows by that time I believe, but if you bought a V6, keep the wagon to swap in the powertrain.