You read up very much on wiring harness here on the BB and it will make you paranoid if you own an 85 or 86 model.

The large grey connector on the firewall on my 86 was a mess when Inga moved to my house. Had several other wires under the hood with crumbling insulation including the windshield washer motors, Dryer, and AC Compressor. Reading about all the issues here on the BB convinced me that my main harness was about to go. Found a factory harness (still had the Volvo tag and part number stuck on it) down at the PUP in an 85 and grabbed it. There are actually two engine harness by the way. After getting it installed and getting the distributor replaced (busted the connector getting it loose)the car ran the same. Pulled the stiff grease covered main harness down and decided to check it out. There was not a single wire in that harness that had an insulation issue and that was for sure the factory harness (Inga has been in the family for 24 years almost). The smaller under the block harness had issues with just the four wires from the center connector on the firewall. Those four wires are important (Alt, Oil Pressure, Engine Temp, and Starter) and they did need to be replaced badly.

Still have to clip and replace wires under the hood in harness that comes out of the drivers side firewall from time to time. Found and fixed a couple of crumbly wires on my main fuel pump replacing the filter this past year.

Bottom line is, give the harness a quick look places like where it passes though the intake manifold. If your insulation is solid then you can relax, clean your flametrap often, and enjoy your car.

Regards,

Paul