I am so sorry I haven't gotten back to you sooner. I haven't been on the forum for a while. Yes, you are correct: the toggle switch is for turning off the propane detector if the camper were only on battery. Since the battery is charging while plugged into my tow vehicle, I didn't want a draw on it then. Also, I do not camp without shore power. If the power ever went out at a campsite, I'd use the battery, but this enables me to turn off the propane detector if desired to conserve.
The toggle switch is mounted in the storage space under the sofa/bunk seat. A little hole was drilled in the wood storage space partition to place it. As far as the hook up of the switch, I'd have to ask my friend as he installed it.