Dash Radio/dvd not working on house power

I am helping out the owner of a 2014 Georgetown XL gas coach parked next door. The dash dvd/radio will not power up unless the key is turned on. If the dash radio switch is engaged no power. This happened after the owner was replacing the antennae booster with a Winegard HD amp and reversed the 12 volts. The antennae booster has no power as well. I suspect that a fuse is blown but I don't know where it is physically located in the coach...I think it may be P4 F1. Help is appreciated!