The symptoms don't match exactly but there was a problem in the '92 models with the Body Computer. It would lock up due to voltage spikes resulting in loss of dash lights, gauges, chime, interior lights, and I think door locks. I suppose that could affect a late production '91 model, but I'd be real surprised if that problem wasn't taken care of a long time ago. The computer could be reset by disconnecting the negative battery cable for half a minute, but the problem typically reappeared within 5,000 miles.
The permanent fix was to replace the Body Computer with one that was less susceptible to voltage spikes, and to replace all relays that didn't have spike suppression built in. There could be up to 12 of those relays but I usually found only four to six. They are located by the fuses inside the van, under the steering column, and they have part numbers that end with a "1001". I think you have to remove the "knee blocker" to get to them. That's the thick panel under the steering column.
I don't know if Body Computers were used yet in '91. If it was, once that knee blocker is removed, the computer can just barely be seen slid in to the right and under the radio. It slides out to the left toward the steering column after removing one or two screws.
If there's no IOD fuse in the fuse box under the hood, (or if there are no plug-in fuses under the hood), look for a smaller cable leaving the battery positive post. It will have a bullet-type connector about a foot away from the battery. That is disconnected when the vehicle is going to be stored for more than three weeks. It removes voltage to all of the computers to prevent their memory circuits from draining the battery. Many functions will not work, but the engine will start and run and some features such as power windows will work while the engine is running. The delivery truck driver can operate the vehicle safely without having to plug that cable in.
Monday, August 1st, 2011 AT 11:06 PM