Oil pressure switch

[North Idaho 5.oh]

Working on a 2003 ranger 4.0, auto, 4x4 ex cab

Ok, so I’m having a weird issue here…. All gauges work with the exception of the oil pressure gage in the dash. I know it’s a “dummy” gage, but it’s got me all sorts of confused.
I’ve switched out 3 known good oil sending “sensors” and none of them work.
The gauge itself only moves up about 1/4 inch or less only when I power the truck on.
I pulled the pigtail off and ran it straight to ground and still nothing…. I even went as far as switching out alternators because I heard that it “could” be a reason for the gage not to work….
Swapped out gage cluster with a known to be good one and still…. Same thing.
What could I be overlooking?
It’s got oil pressure, otherwise it would have blown up by now… I’ve driven it about 100 miles with the gage flat lining.
Any help is appreciated….. this is the first time I’ve ever dealt with this…..

 

[Uncle Gump]

Likely an open in the signal wire.

 

[89longbed]

Anyone know what the voltage is suppose to be at the switch? There's the resistor built into the guage (or PCB) that causes it to only go half way to the right. At least that's how it worked in the Gen 1 Rangers with the dummy guage. That resistor and the guage should cause a specific voltage drop.