Sounds like a short. The starter wire; somewhere in the circuit(s) that involve the starter are shorting out. Had a similar situation. Turns out the wire from the start button was shorting to a cross rail under the dash. Would hit the button the the voltmeter needle would rapidly go to zero.Sometimes the starter on my Big block won't do anything except kill the power. No click or anything. I'm thinking all the brushes aren't contacting. I took it off to disassemble it but can't get the chrome cap off to look at the brushes. Is there a trick to removing the end cap or do I have more problems than I thought. I have all 4 bolts out of the end cap. View attachment 619436