Try tightening all your connections. I had exactly the same problem. Turned out to corrosion (can't see it) or slightly loose connections at the bus bar in the battery compartment. Also clean and tighten battery connections and common ground on the wall. After tightening all worked well.
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2012 Redwood 31SL chasing 2019 Denali HD 3500 Duramax SRW
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