I think it is a real shame too, as I think that this is one of Mercedes nicest looking sedans- only 2nd to the 1981-1991 S-Class sedans.
Hope you get all of your electrical problems worked out.
It sounds like an electrical short in some wiring. I have heard of a lot of electrical problems with the 1992-1993 S-Class sedans. I was considering one a while back and passed on it because of this. I have seen a couple of these on E-Bay that had caught fire due to electrical shorts. One caught fire at the battery and one was under the hood.
Like someone else already said- just pull the fuse to the heated rear seat.
1993 Mercedes 400SEL 4dr
2012 Honda Civic LX 4dr
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville 4-dr hardtop sedan
1988 Mercedes 300SEL (was mine, now mothers)