There's a procedure I've been using (and teaching) for over 50 years called a "series resistance test" where a low-reading voltmeter (2 volts full scale) is used to check the voltage drop across every connection in a starting circuit. The process is a little too complicated to type, but if you'll get in touch by private message, I'll share a phone number for a 1-on-1 conversation. I learned the tricks of the trade about maintaining starting systems back in high school in the 1960's, when I was driving a 47 Mercury flathead V8 with 11:1 compression and a 6 volt starter!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!