Ducted Vacuum Inlet Valves

All modern ducted vacuum inlet valves contain two low voltage metal contact points inside the hole of the inlet valve rather than a single ball bearing switch or micro switch on the inlet flap. These 2 pins are required to allow a ducted vacuum switch hose to work.

All modern ducted vacuum hoses have metal contacts or a ring on the hose cuff to make contact with these 2 pins which turns the vacuum on. Older hoses with a plastic hose cuff (no metal contacts or ring) will not work with the modern inlets. You can replace the ducted vacuum plastic hose cuff on your old hose with a cuff with a metal ring and your hose will now be compatible with new and old ducted vacuum inlets.
When replacing inlet valves never remove the connection screws completely because the pins are spring loaded. Undo screws slightly, wrap low voltage cables around screw and then tighten screws.