So I'd be curious what might be the place to look for the cure to a total electrical cut out in a 1995 940 T?

I was in the grocery story parking light, (with bags full of frozen food) when my heretofore trusty Volvo 940 failed to start.

First the steering wheel & gear shift was locked and the ignition wouldn't budge. But pushing the 'unlock' button on the transmission got the steering wheel to turn and the gear shift to move. No fuses burned out.

I suspect it's the electric connection down on the transmission mount? I had a similar problem with my old 1980 240.

But oddly... after going to to a payphone and trying to arrange for my spouse to come pickup the frozen groceries I was gone for 5 minutes. When I returned to the car, the electric was BACK ON. The parking lights were blinking and the shopping mall security car was circling around... very suspicious!

What would cause this mysterious electrical disconnect to first of all go OFF and then to come back ON by itself?

I'll probably call my indie mechanic... but I'd like a bit more knowledge to go on if possible.