Bad amp gauge

Heh. Suppose should have asked before typing all that.
What is the problem you are observing with the gage? and why do you think that is the cause of the no start?

During start the gage should show very slight discharge. About the same as when stepping on the brakes, less than when turning on the headlights.
If the gage needle moves as expected when stepping on brakes or turning on a light, then the circuit through the gage is probably OK.

If the gage and any connections show the type of damage pictured in the link below, that's another story.
https://www.forabodiesonly.com/mopa...is-connector-is-called.484853/post-1973348967