Welcome to the forum
The battery meter on the monitor panel is not accurate, you need a true voltage meter. You’ll notice if your not plugged into shore power, as you add load the number of lights will go down, turn the loads off and the lights come back on. When you say you got a “plug in” meter, where does it plug in?
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.