I reread what you just said. I have installed a new fuel gauge as of today because I was told it might be the issue. But if you were saying the ivr is built in with fuel gauge then it can’t be that.
This will give you info on the IVR. RTE Gauge Faq - rte
I would use the multimeter and start checking the gauges and wires but it's unusual for all of the gauges not to work unless it's an issue by the pins or a bad ground somewhere.
