had a similar prob in my 85 300D and if yours uses the same fuses (and mine were alum) i'd check that first, they can look completely normal

spun the fuses one at a time and when I got to the right one my gauges and windows worked again

pitting/corrosion (oxidation??) at the fuse-box even if only one fuse is affected can wreak havoc

good idea to keep that fuse-box in tip top shape, cleaned it all up (the contact points) with light sandpaper and a wire brush, suppose dielectric grease wouldn't hurt