when it rains it pours

Well, I feel your pain. I'm currently driving my motorhome for basic transportation. Subaru daily driver died the head gasket death. Not worth repairing in a 300K 10 year old car. Just retired, so my company vehicle was turned in and we're planning to move back to Saskatchewan in a couple months. Holding off the car purchase till we get settled.

On your wiring problem, you likely do not need to make a wire by wire inspection under the dash. Any issues will be obvious. Bubbled or melted insulation merits further investigation. Do be careful when you power everything up after installing your new harness. That's the time issues will show up. Bulkhead connector is always a likely suspect. I don't think loose field wires on your alternator would have caused the fire. Whatever did is likely burned up in the engine harness and will be replaced anyways. Take your time, clean everything up and run wires carefully, make sure everything is secured properly and won't rub or fall onto hot components. Not sure what sort of ECM you expect on a 40 year old car. Are you referring to the voltage regulator?