On some coaches if you hit the house power switch more than once it can toggle from charging to not charging the house batteries with the shore power plugged in.
You will need to put a voltmeter on the house batteries and toggle the switch to see when the voltage jumps over 13v.
On most Class C’s the shore power does not charge the chassis (engine starting battery). You can install this to let the house batteries keep the chassis battery charged when the motor is not running and you are plugged into shore power.
http://www.lslproducts.net/TLSPage.html
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