1991 buick roadmaster /after raining car won't turn over.
check all the battery cables/grounds to frame/engine and wires...hummmm
Yep! Sounds like a bad connection. Really look hard at the engine to frame and body to frame grounds. Depending on the climate you live in those will rust real bad and loose conductivity. Also check relay on the top of the starter those connections could be loose or corroded as well.
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