The pump has a pressure switch at the outlet to shut it off when the system reaches a preset pressure. If you have no water in the system, there will be no pressure to close the switch and the pump will run until you turn it off at the control panel. Sounds like it is working as it is designed to.
As for accessing the pump - most come with a couple valves and a clear, flexible hose for drawing antifreeze from a jug when winterizing. If yours does not have a winterizing kit, you can purchase a fitting, with valve and suction hose to install on the pump inlet that will let the pump draw from the jug of anti-freeze, instead of the fresh water tank. So unless you want to pay your dealer to winterize, you can access it and do it yourself.
2015 Jay Flight 32RLDS Elite
2012 Chevy 2500HD Crew Cab LTZ (6.6L Duramax/Allison)
Equalizer Hitch (1200# bars)