Engine cranking, take a reading across battery posts. The generic specs, says it shouldn't drop below 9.6 volts. If it drops way down, need to charge battery or replace.
Also, with key on, no crank, you can compare voltage readings across battery posts and B+ at the ignition module, I think both readings should be close to the same. Before I did anything, I'd have to check feed to and from the ignition switch. I wouldn't tear out no wiring, till I was positive about the problem??