Ammeter to Voltmeter...who does it?
I pulled this off the internet, but it's just like mine. Is this the IVR?
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OK, focusing on the fuel gauge... One of 3 studs has the noise suppression cap' added on it (prevents noise in radio speaker) The wire in the harness connector there (in line with the harness connectors locator) is switched 12 volts into the Mechanical limiter inside the fuel gauge. Top center stud with a square hole in the board and strange clip over it is the pulse voltage for the fuel gauge and the temp gauge. Lower right stud is connected to the fuel sender wire (should be a blue wire in the harness connector there).
Small details... The square hole in the circuit board and strange clip covering it and that stud is all about ventilation/cooling. Two resistor windings inside one small gauge can is a good bit of otherwise captured heat.
The engineers later determined that all of this wasn't really necessary. Later examples such as 67 up rally panels had a notch cut out of the top of the gauge can (heat rises) and a Bakelite cap over that warm stud through a typical round hole.
The more you know... Notice the temp gauge has only 2 studs. That is a common gauge. The only current path there is from stud to stud. Only path to ground for the pulse voltage is at the temp sender. The fuel gauge has 2 studs that serve the same purpose. Pulse voltage from limiter goes to ground at fuel sender.
So with the switched 12 volts also going into that gauge, where does it go to ground? Lift this gauge from the instrument panel and look at its backside. There is your 4th connection. A small strip of metal contacts an unpainted spot in bottom of the housing to provide a chassis ground path for the mechanical limiter.
There is a simple way to disable and isolate the original mechanical limiter inside that gauge and add on a solid state regulator but since so many members here are soooo quick to point you to the RTE website and their instructions to open the fuel gauge and bend something, I regress. Good luck
