My cig lighter gets it 12 volt from the chassis not coach. I found my fuse under the dash on the driver side, buried in a nest of wires. Not saying yours is in the same place but I am sure your fuse would be off the the chassis.
1997 Triple E Empress, Freightliner Chassis, CAT 3126 w/ 275 horse's.
MD 3600 Tranny, 2011 Ford Escape Hybrid w/Blue Ox tow bar and Roadmaster Base Plate.
Amsoil Synthetic Oil only for my baby.