NYYLON gets the prize for the best and most correct answer! Many thanks. The thermostat wire was located next to the forward slide out switch in the forward cabin. After removing the slide out switch, and looking really hard, I spotted it about 8 inches to starboard. A little fishing and out it came, along with the +/- 12VDC wires also needed.
I did a temp wiring to see if it all worked, and again NYYLON was correct, icebox. Tomorrow I will wire it permanently and finish the AC trim work. For those wondering about installing the unit, excepting the time spent looking for the wire, total install time is about 4 hours, including the hour necessary to remove the old skylight and caulking around it. Hats off to JAYCO for the perfect rough in.
The bad news is I discovered a few new projects. While looking for the thermostat wire I removed a ceiling speaker to get a look around and discovered why they sound tinny. New upgrade speakers on order. I also pulled the shelves out of the forward wardrobe because Jayco had said the wire might be behind a removable panel. So I removed them. 8 screws. BEHIND them (actually forward of them) is enough space to store things that you like hidden. Drawing up plans now.
Thanks for all the great replies.
23 days till the summer road trip: Cape Cod to Utah. Plenty of time!
2015 Jayco 345 BHTS 5er
2012 Ram 3500 DRW CC Longhorn