Most OEM's install a solenoid that is activated by the Ignition switch when on or engine running. They control certain 12 volt items that seem to be chassis items but are really items installed by the RV coach maker. Some of these items
1. Back up camera
2. Dash radio/GPS
3. The slide out disconnect system
4. dash AC/Heat
5. wiper blade power
6. side view power mirrors
7. some others, but these are usually the main ones.
As other have stated, that solenoid is either stuck CLOSED or somehow the IGN power for it is ON all the time. Doug