The circuit is listed as "LR." The secret decoder ring ("Wiring Identification Guide"- link here
FROM: BATTERY MODE SWITCH (AUX START SWITCH)
TO: BATTERY MODE SOLENOID (AUX START SOLENOID)
That switch has three wires: KE (ignition-switched input), LS (house battery input) and LR. It would be reasonable to assume that in the absence of an AUX START SWITCH then LR is actually spliced to KE. If you look at the Chassis Wiring Installation diagram, you'll see KE is tied to the Ford fuse panel under the dash. I would track down the fuse, remove it, and see if LR goes dead.
Also, you'll have to pick up a source for LS to install a typical Winnie AUX START SWITCH.
It appears as if Winnebago started installing an AUX START SWITCH in the shorter Minnie Winnies in 2016. The panel is on the dash, somewhere near the center.