Also, as you check along the wires, if you find a suspicious area, look for a voltage drop when the starter solenoid/switch is engaged (if it is even doing so).
I cleand up a couple voltage drops on the old Gulfstar
that were only apparent when the starter was powered (by pressing "start" button). The reason is that the voltage drop was small when a small current
was applied, but large when the large starte current
was applied. It wasn't apparent with a meter, unless you had the starter motor
running and/or circuit energized.
My problem ended up being a starter installation
issue (previous owners!) so I cleaned up the circuit for no reason. But... on yours, as you work through, make sure to look for those voltage drops to be sure. Good sanity check.