[xwsarebset]

The early falcons from xk to xp and the compact fairlanes had a voltage regulator fixed to the back of the instrument cluster held on by one screw. they had two wires attached and the case was earthed to the dash by the screw. the xr xt xw etc had the voltage regulator built into the temperature guage. I think from memory the voltage was kept at 6 volts. to test the guages you would use a 1.5 volt aa battery should read quarter on fuel guage.
The voltage regulator for the xk to xp and compacts guages was from about an inch long on some and about two and a half inches long on others.
Hope you find helpful.