Mystery Electrical Problem
 

I have what is apparently a bizarre, though intermittent, electrical problem. Sometimes when the car (91 Legend) is started, none of the following works: tachometer, spedometer, radio, windows, brake lights, turn signals, or gauges.

The lights, radio, power locks, and sun roof do work.

Sometimes a bump in the road or slamming the door will make everything come back up.

The dealership and a couple speciality shops are all talking exploratory surgery to find the problem.

Any suggestions or advise to expedient the hunt?

Thanks.