Yup, if your factory gauge moves, the switch is working properly.
...but if your POS factory oil pressure gauge DOES fail, it's most likely a bad switch/sender unit (located next to oil filter). Mine went bad, so I replaced it with p/n 1U5Z-9278-DA
. Thank god I was running an aftermarket oil pressure gauge. LOL
I found this reference the Bullitt Archive website, linked below:
Main site: http://www.bullittarchive.com/html/
Listed under "Special Service Messages:"
R&R oil pressure switch F8AZ-9278-DA with 1U5Z-9278-DA
Some 1999-2001 Range, Explorer/Mountaineer, Crown Victoria/Grand Marquis Town car, Mustang, F-150, Super_duty F-series, F650/750, Expedition/Navigator, E-series and Excursion may exhibit the oil pressure gauge registering low or no oil pressure usually on initial start-up after several hours of cold soak. Verify the gauge/wiring are functioning properly and verify the engine does have proper oil pressure. To service replace existing oil pressure switch F8AZ-9278-DA with 1U5Z-9278-DA. If any engine oil was lost during removal and installation refill to t appropriate oil level requirements reference your appropriate workshop manual fo rcomoplete service procedure.