My propane gas detector would only work when I had the main switch down in the battery mode.

It turns out, the factory wired it to the battery side of the switch (the switch & the detector are next to each other in the dinette bench).

I ran a 14 ga. wire across the underside of the floor in a waterproof conduit from the detector to the 12 volt fuse block (next to the convertor) with a 3 amp fuse

Now the propane detector works on 110 volt park power or 12 volt battery power

Les 97 21' Towlite