1) Switch is set to be persistent
2) On the vault gear door's "Activate Paretnt" tab, right click then "New". Select the swicth by picking from cell & persistent ref lists or use "Select Reference in Render Window" and when hovering over the swich, the cross hair turns from red to white - double click on the switch.
3) Optional - Check the 'Parent Activate Only" flag if you only want the switch to open the door, and not by clicking on the door itself.