I can help with one question. The Chevy used a capillary tube type gauge so that's why there's no wire for it.

I, too, would assume the different polarity is why the gauges are marked.

the tag sounds like a rebuilder's tag to me.


"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.