In my previous posting I told of my experience of a fire on my 91 740 Turbo which, I thought, was caused by deteriorated insulation in the wiring harness. The insurance appraiser and the repair shop determined that it was started by a short circuit in the electric cooling fan which caused the wiring to overheat. It damaged the harness all the way back to the fan relay and the relay itself. According to the wiring diagram, it appears as though the control side of the relay is fused but the power side is not. And there is a direct line from the battery to the relay. This line is part of the harness (part way along at least). It's obvious that a short in the fan wiring could melt the harness so that a direct short from the battery to ground through this wiring can cause a fire like I experienced. To stop the short, I had to disconnect the battery, it wasn't good enough to turn off the ignition key. Maybe it would be a good idea, as Steve suggested, that a fusible link or fuse should be in the power side of the relay. Anyway, I'm glad it wasn't a problem with old and brittle wiring insulation because all of us with older Volvos have a lot of miles of wiring in these things.
Thanks to everyone who offered advice. You guys are great.
Dennis