I have a somewhat generic wiring diagram for the manual control of the DeWald manual leveling system on my Tour Master that shows the parking brake switch lead (white/orange wire to pin number 3 of the harness to the control panel for some of the older units...pin 1 on my unit controller which is #140-1179) that is supposed to be grounded when parking brake is ON. For my coach, when the engine is running and the parking brake is OFF the jacks retract even if the control panel is not turned on. Maybe you have a break/open in that circuit or its equivalent...
You can download the documents from the Power Gear website...
http://www.powergearus.com/products/leveling-systems
Chuck