I'd make sure the connector is good. After 27 years the contacts can become slightly corroded loose etc. This is the first thing I check when I have any problem involving electrics and it's been the problem probably 80% of the time. I bend/twist the males slightly and tighten up the females and reconnect before I go running out and buying parts. Occasionally I've tinned the male pins.
Low voltage and high resistance messes everything up.
Things that were fine but had less than adequate connection and were giving problems: TPS, Cruise Control, Fuel pump relay, Hot wire kit and the hardest one to find the turn signal connector on top of the steering column.