Thanks for all the additional information + the great fotos!!!
The sender in your pic is indeed the correct one and is identical to the one I obtained from AutoZone, their part number #PS143 (Manufactured under the "Wells" line).
I did not have the pigtail shown in the pic......the seller of the used parts cut the pigtail just south of the connectors for the gauges so at least I had the connectors to splice into my "shadetree" wiring job. Aside from that, I'd have never found the original connection point for the pigtail had I obtained one, because like you noted the connector is well hidden behind the heater and (in my case) the Air Conditioning system.
I'm well aware of the "floating ground" system that's designed into the dash lighting system by Nissan where the variable ground to the dash lights is wired through the rheostat dimmer knob next to the cigar lighter. I learned that (the hard way) from the guy in the car radio repair shop when I tried to return the newly repaired radio to him for rechecks because I couldn't make the dial light in the radio function. All is good now that I have the original AM/FM radio wired correctly.
For the gauge lighting.... I chose to "tag on" my wiring, using 2 of those very "Mickey Mouse"
blue "Scotchlock" fold over connectors (more later about those).........to the existing wiring for the shift quadrant illumination, since I already had the console removed to install the gauge bracket on it's backside.
Believe it or not, I am a retired, certified ASE Master Mechanic and normally I despise those fold over connectors that squish into the wiring to make a connection.....having previously found them, in other installations, to be the cause of failures in other instances.
It may help to know that I'm now old (68) and severely hampered by ached and pains from arthritis and I have extreme problems crawling around the truck to do the work.
I intentionally chose the factory style sender with duel circuits so that I could install the sender directly into the engine block oil port without the use of a tee that other folks have seen break off later from the weight of the sender and or switch hanging off it.
As a side: I'm disappointed that I purchased this truck because I thought it would be "plain, simple & easy to work on. Boy was I mistaken.......even though this is a tiny 4 cyl engine without fuel injection........I find it heavily endowed with required emissions controls (all connected & working as designed) it seems nearly impossible to get a big beefy hand in anywhere to work on anything without cutting ones arms to shreads. (Old people have only very limited patience for these things).
I had a difficult time wrenching that sensor into the engine, because I didn't want to remove the oil filter for access room creating a big oily drippy mess on the side of the engine & I don't have a 14mm or 9/16" crows foot and even if I did, I doubt it would provide a long enough "reach" to get outside the sensor can profile for installation of a requires socket extension. I'm praying that I managed to get it screwed in far enough so it doesn't fall out or break off at the thread until the next time I have the filter off for routine Mx,