Must have been tired last night...
I ordered the replacement wire last night based on looking at the wiring diagram...
AV3 is not 3ga... It's more like 12ga!
Should have used my brain looking at the actual wires.
Luckily I've got lots of 12ga wire and fittings here. The 2ga stuff is going back, or I'll add it to my stock for future projects.
I went through the rest of the small wires in the loom tonight and it looks like the wire to the solenoid got the worst of it and I'll replace it.
The rest of them have a few wear spots in the insulation so I'll electrical tape and/or heat shrink those spots before heat shrinking the whole lot together again.
I'm tempted to seperate the wire going from the starter to the main switch and the wire going to the glow plugs from the rest of the auxiliary wires to keep this from happening again for the future owner in 60 years.