HELP! temp sensor wiring

[Beaniemoo]

Right, doing the 172 into valver project, but the 172 temporature sensor wiring has got me really scratching my head!
The valve has a seperate temp sensor for the temp gauge, 2 wires, 5 volts in one, 1 volt in the other simple as you like.
But, the 172 has 3 wires in it! 2 in from the ecu, 5 volts in one (black or white), nothing in the other (white or black), simple again but thats for the engine control unit to know the temp, the third wire (beige) has me scratching my head. It goes off to the plug for the body loom, so presume its for the temp gauge.
Only thing is I can't get the temp gauge to work! I don't get how the gauge could work with only one wire!
Anyone know how the gauge works on a 172? Or what the 3rd wire does?
I don't really want to run a seperate temp sensor as thats a bit lash, when I wired the gauge upto that ecu temp wiring it worked but the fan was running constantly and the oil light was on , and any other combination I got nothing!

Thanks for looking

 

[benji&eka]

i'm sure on the 172 it has just one sensor that runs the gauge and the ecu inputs. but i dunno bout the wiring

 

[Beaniemoo]

I'm pretty sure it has got 1 sensor for both as its the only sensor in the cooling system.
The thing is I have 2 wiring diagrams for clio, but neither are for a phase 1 172. One shows a sensor with 2 wires, one with 4! I've managed to wire in the rest of the car fine, I'm handy with electrics but this one has really got me for now! I'm sure I'll get it sooner or later (I don't have any choice, we can't run a track car without a temp gauge). Just wondering if anyone knew.

 

[benji&eka]

sod it and put in an aftermarket gauge