Hz wagon fuel gauge mystery

[lcgtr1970]

Hi guys.
I've been having issues with my fuel and temp gauge not working ony wagon. I swapped the gauge over with another and it still does nothing.
Now in my fiddling around I noticed this plug. It seems to come from the fuel and temp gauge cluster and pokes thru a hole towards the back of the cluster of red lense lights in the middle of the dash.
But I can't find anywhere that it should plug into. Would this be the reason there's no movement or back illumination of the fuel gauge?
If so where's it go?...(it's the brown 3 slot plug)
ThanksDSC_0788.JPG

[Big Rob]

What colour are the 3 wires attached to the plug? A factory wiring diagram will sort it out.

[lcgtr1970]

Grey. Black, and orange

[Vombil]

it does nothing. test to see if you have power there and then work backwards. all the best

[ambientgoat]

Sounds like you need to investigate the sender to me. Getting a new sender is as easy as ringing classic oz wreck, rare spares or similar. Removing the tank in a wagon is a pain.

[Spike]

Have you checked that the wire hasn't come off the temp sender and is shorting out on the engine block? [ this happened to me and caused the petrol gauge to read zero]. No back lighting might just be a blown globe?

[panoz78]

Gray ......dash light illumination
Black........earth
Orange.....ign/acc power
The plug could be a spare for clock ,rear window Demistor etc
To test gauges
Leave pluged into the car
Turn ignition on and disconnect temp wire at motor
Put a multimeter on the wire (green)
It should get pulses of up to 5v
Then do the same with fuel gauge at the tank .(think its Tan from memory)
If you don't have a multimeter use a test light .it should light up dimly and pulse
If. All that happens gauges are OK
(This method can be used for oil pressure gauge on GTS dash)
It is possible for the plug in the pic to be of your gauges
With that dash from memory the 5v regulator is in the gauges ,if you don't get the pulses the regulator is dead or there is no power to the gauges..

[lcgtr1970]

ok...
So I tested the wiring that plugs into the temp/fuel gauge and there is power there. I Upgraded the old thermal voltage regulator to a solid state regulator which fixes the issue of the old one frying... ( link here>>> http://holdenpaedia.oldholden.com/Fuel_Gauge ).
This has fixed the issue of no back light illumination, but there is still no movement in the gauges.
So... Sounds like an issue with the sender now? Is there a wire that leads from the sender that could be disconnected anywhere?
Thanks guys.

[gregbark]

A possible check of the fuel sender itself. Remove the complete sender. using an Ohm meter attach one wire to the terminal that goes to the gauge and the other wire to the circular plate as an earth. Moving the float up and down slowly ( replicating a tank of fuel being used) should show a reading. It should show 73 empty to 10 full. take care of fuel and sparks.

[panoz78]

Checking for voltage at the sender end of the wire also checks your wiring.
Start with the easy one first(temp)
The 5volt regulator has nothing to do with the gauge illumination