power

[TurnerFam]

a Palazzo has 6v batteries wired in Series and then in Parallel to provide 12v power to the fuse panel and the Inverter.

If you did not use the 'Store/Use' switch to cut off the power while in storage, likely any draws sapped the batteries, to the point where the Inverter will cut off automatically, if you didn't cut it off to begin with.

The Inverter will only come back to life when it reaches approximately 12.5 or higher in voltage.
The 12v lights and fans can operate on much lower voltage, but until the batteries are back up to the 12v or higher, likely you'll not have everything working properly.

When you plug into shore power, the Inverter's built-in CHARGER should try to then charge the batteries, but the Magnum charger is not an emergency low-level charger, and therefore probably will not be successful... a more typical stock battery charger would be best - attach the RED Positive lead to the Main RED battery post, probably in the front left area, and attach the BLACK Negative lead to the Main BLACK post, probably in the opposite corner REAR area - where you see it's cable going to a metal GROUND on the vehicle itself.