Dropped 1.2 volts between battery positive and the fat red wire on the alternator? Wow. Seems to me that the drop there should be close to zero.

You give 3 choices of things to check;

1) Wire from alt to starter

2) Wire from starter to battery

3) Fuse holder.

Number three is not relevant. Fuse (the 23 amp, right?) is not involved.

Number one is not likely. Even with the under-engine harness being messed up that wire was OK. It is a PITA to open that harness and check out

Number two - there's a possible. Corrosion from around the battery terminal can work its way up inside the blue insulation.

One "fix" is to clean the cable terminal. Do this with great care, as if a drop of the liquid gets into a battery cell, it's dead. the liquid can fizz up a lot, too.

Use a glass container, like a peanut butter jar. (Well, I suppose plastic would work.) Fill is half up with water, and dump in a tablespoonful of baking powder. Have another container with just water. (The rinse)

Remove the positive battery cable from the battery terminal. Hold the container so that its top is below the level of the battery top. Dunk the cable terminal in the liquid, an inch or so deeper than where the insulation ends. Hold it in there til the fizzing stops. Then put it into the rinse for about 15 minutes. Swish it around.

Let it dry for 30-45 minutes. Use a hair dryer on it, if you can. Hook up and test.

Good Luck,

Bob

:>)