Davey, my wife read your post, and reminded me of something I told her nearly 40 years ago when we were dating:
"Once, long ago, I thought I was wrong, but I was mistaken!"
She says, no, I never get tired of being right! Now, that's not my opinion, just one from "she who must be obeyed"!
Glad things worked out well! Yes, any loose or dirty connection, either hot or ground, adds resistance, and a 6 volt system just doesn't have any voltage to spare to overcome it. That's one of the main reasons the manufacturers went to 12 volts in the mid-1950's- - - -there's more room for error with twice the voltage available.
Jerry