Is it and 85? Those wiring harnesses were made out of corn starch I believe.
Also check all the ground/earth connections. The key ones are in the engine bay (behind radiator on battery side and the one for the alternator), in the dash (on the big bar joining the two a-pillars together) and in the boot (under the false floor).Any blown fuses anywhere? Sounds like the battery power is partially not getting places. Do check for solid battery + switched power at the ignition switch and go from there.