1963 Valiant Instrument Panel Questions

If the fuel gauge has 3 terminals, the IVR is built into that gauge

How it works

External IVR plugs into the circuit board, has a ground, and receives 12V from the key. It "chops" the 12V (original type works like a flasher) to approximently 50% duty cycle. It feeds this power to the gauges, through each gauge, and to the gauge sender to ground.

The difference in the Ralley clusters or the early cars with the IVR in the gauge operates the same except the thing is built in. The fuel gauge receivers 12V from the key to one terminal, which feeds the internal IVR. The IVR internally feeds the fuel gauge, which then has a sender terminal stud

The 3rd stud is the IVR output, in parallel with the fuel gauge. This feeds the IVR power OUT of the gauge to the PC board trace, which then feeds that IVR output to the temp and oil gauge.

You can replace it by abandoning it and adding an external. RTE is on outfit;

https://www.rt-eng.com/index.php/RTE_limiter.html
https://www.rt-eng.com/index.php/RTE_Gauge_Faq.html