Turning key to "run" causes all power loss.

Mattax said

How much current, if any, went through wires for the volt drop test from the battery to alternator?

If your car has 8 gage wire, then it has the 'fleet' or the optional heavy duty wiring that came with rear defrost grid cars. The charge path is a bit different for each of the three possibilities. Lets try to establish which of these the car has before trying to pinpoint the problem location(s).

Posting photos will make it easier for us to help.

Click to expand...

During the initial key-off voltage drop test, I'd assume that nearly zero current was flowing.

Switching the key to "run" caused the blower fan to come on (it was set to Lo speed) and possibly the interior lights (driver's door was open, most of the lights have LED bulbs in them, so low current there), plus whatever quick in-rush of current to the ignition coil. All said, the current was fairly low, but I quickly found the hot spot going into the fusible link. I'm still waiting on my wiring and parts (should be here today) to complete the rewiring. Then I can proceed with the voltage drop test (again) and I'd like to include turning on the headlights.

I do not believe that this car has the rear defrost grid. At least, I don't see the horizontal lines on the back glass that I would expect to see. In my inspection of the schematic and this car's wiring, I haven't come across the indicated wiring that would lead me to believe that this car was ever equipped with the defrost grid.