The water heater switch is located in the control panel right next to the door so I don't think it is that.
I just called an EVO dealer in north Texas and he couldn't tell me over the phone and said I would have to come in for them to trace it.
I thought it might be for heat tape in the underbelly, it has the climate "B" package, but the dealer told me that the heat tape should come on with the furnace so it probably isn't that either.
John & Theresa
2014 EVO T3250
2002 GMC Yukon 2500XL SLT 4x4, 6.0, 4:10
Husky Centerline WDH w/sway