The EFE-TVS vac port screws into a ported thermostat housing (some call them "water neck", others call it "water port" or "water outlet"--whatever works) At the current time I have the sending unit for the electric fan installed onto it as I have not had the chance to get the EFE-TVS check/delay valves installed. My fan clutch started making horrible noises. It was a great time to try out this electric fan set up I bought for my 76' 4x4 Cheyenne blazer and never installed. The wiring kit is an always on kit (when ignition key is turned on the fan powers on, fan/relay powers off when the ignition is turned off). I added the sending unit to see if there was a difference. I may get a dual port thermo housing, but there is not much difference in the operation of the fan with the exception of the 5 minutes the fan isn't on when starting. I don't want to spend too much time on the electric fan here.
When I remove the fan's sending unit the EFE-TVS will go in the sending units place.