My 1979 245DL had problems with the under-engine-front harness, but it was the failing insulation for the alternator wire and oil pressure sensor.

While inside that harness, I could see just what lit your fire.

The alternator charge wire carries the amperage to the battery. but actually that wire just goes to the starter. It connects to the same stud as does the fat red wire from the battery. So - there is heavy battery amperage present in that under-engine-harness all the time.

The 1979 245DL had that harness held in place by two metal tabs that were bent into place. The rubber covering on the tabs was wearing off. Once gone, the tabs become little saw blades, cutting away at the harness covering, thence into the inside wires themselves.

When a tab cuts into that fat red wire - BZZZAPP - giant short circuit fed by full cranking amps, rather like an uncontrolled electric welder.

Next to oil and oily road grit - plenty of nearby fuel to get the fire going.

I like the commect about the harness from Dave Barton running inside a water hose. Worth converting all the daily drivers I now run.

Regards, and yes, I am sure that even if you had the marshmallows with you, it wouldn't have seemed appropriate to toast them over a Volvo fire.

Bob

:>)