The heater needs 12 VDC to operate the ignitor. You'll need to decide where to mount the switch in the bathroom, too. I used a coathanger to fish it up into a plastic cabinet and used the template to cut an opening for the switch. I'm reasonably pleased with the way it came out.
Good luck. Take your time, and you'll be fine.
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto