Wiring for an oil temp sensor - something odd happening

[RobPhoboS]

Back in 2017 I wired up an oil temperature sensor, and it was working without an issue (old thread here: https://www.350z-uk.com/topic/114588-wiring-in-an-oil-temperature-sensor-for-the-inept/ ).
The way it's wired up is tapped into the passenger side cigarette lighter wires (red/black), and the socket itself still works (ie phone charging), as well as the gauge working with ignition.

However since then I've just fully rebuilt the engine and moved the single-wire sensor from it's original place onto the mishimoto sandwich plate.
After moving it, of course it stopped working. 
So I bought a 2 wire sensor, that didn't seem to work (grounded it to the engine block), and then I bought another gauge kit just in case the gauge itself was on the fritz.
Swapped over the wiring to the new gauge (comes on with ignition), and thought I'd test the new single wire sensor (that came with the new kit) out first by dipping the end into hot water, and nothing happens.

Nor does it work with the old sensor that's still in the oil sandwich plate.

I've got a multimeter, and can test away, although I don't know what I'm doing so any pointers would be really helpful !

Tested the sensor with the multimeter, seems to be reading correctly, and changed accordingly when dipped in hot water.
So it must be something to do with the ground wire I guess.

EDIT:
Ended up buying a new gauge (Prosport Premium), everything works as it should do now. Well it did the other night 

Edited August 16, 2021 by RobPhoboS