the parallax 7300 is a converter/charger, not an inverter.
while confusing it is important to understand the differences.
you should have the owners manual in your a/s kit but here is a link to it...
i never use the 'kill' switch while plugged into shore power.
basic the kill switch cuts off all of the small 12 drains (except the lpgas detector) called phantom loads.
the phantom loads discharge the batteries slowly.
1. first disconnect from shore power.
2. move the kill switch to 'store'
3. lower the front cover and inspect the fuses.
4. replace any fuses that are cooked.
5. close the cover and move the kill switch to 'use', do not plug into shore power yet.
6. should have 12v
7. turn kill off again and back on, i usually wait 2 minutes.
8. IF the 12v
is working, plug back into shore power
9. after making sure none of the main breakers have tripped and everything is working, unplug shore (110) again
should still be working. now flip the kill to 'store' again
11. drop the access cover and check the fuses again. IF any fuses blow a 2nd time, you need an expert.
i'm just a user and don't know much about 'lectricity, except to be careful about touching things...
here is the 'trouble shooting' flow sheet for the parallax...
i can't imagine the battery leads have been reversed, unless you've unhooked them recently, but the basic steps to follow for 'no power' are provided..