That's a volt meter for the camper battery. The meter is the type that would go on a forklift or golf cart. I put it there because I run the fridge in AC mode from an inverter while we're driving, and I wanted a way to keep track of the battery state of charge from the cab. I can see the meter in my side view mirror, and despite being a reversed image, I can tell at a glance whether the battery SOC is rising, falling, or holding steady. I can also tell by what the gauge is doing when the fridge's AC element is on and when it's not.

:):)