Check the ground side where the wire is bolted to the frame. RV Manufacturers are famous for painting the frame then bolting the ground wire to the painted surface. The bolt makes contact on the treads for a while, but a little corrosion sets in (doesn't take long) and you loose your ground.
I'm not that familiar with a Hummingbird but if it has a power distribution/fuse panel there are also fuses in there to protect the unit from accidental reverse polarity. Those could also have blown.
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Buddy Ray - Atlanta
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Jayco 2016 Eagle HT 26.5RLS
Ford 2016 F150 Lariat, 3.5L V6 Ecoboost
Max Tow Pkg, 36gal tank
Reese Sidewinder and Reese Titan 16k hitch
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