What resistance readings?
You have an intermittant condition in your charging circuit.

Here's a plan:

Yank on the D+ wire see if the ring lug falls off
wire brush everything on the alternator:(The studs and ring lugs)
1 D+
2 B+
3 Ground wire plus the other ends on the block and the starter motor
Put it back together and maybe add an appropriate size bronze lock washer
at the studs with a tiny smear of never seez to delay corrosion

Post back if things improve.

This shouldn't take more than an hour.

Bill