The largest red wire from the battery connects to a large covered lug on the starter. The large red wire from the alternator connects to that same covered lug. It's a way to get the charging current from the alternator to the battery using less wire than would connectioning that alternator all the way to the battery.

The thin red wire and the thin black wire from the oil sensor should be re-routed, they lose insulation in the under-the-engine-front harness.

Pull the gray connector loose from its mate, and look at it carefully. The back side has a hinge and can be opened. There are but four wires, so it's easy to make a little map of which one is where. In 1988 the crumbling insulation problem was fixed, so the colors should be apparent.

Be sure to re-use the end terminals. They are rare, junk yard item - with luck.

That thin red wire is the only alternator wire needing re-routing. The fat red one seldom gives trouble, same for the ground wire.

Good Luck,

Bob

:>)