Before I crawl under the dash

I WOULD NOT jumper the IVR. NO!!! The gauges work (originally) off 5-6V "equivalent" AKA "pulsed" 12V at about 50% duty cycle.

Not trying to make fun but MAN I don't know why you would not have tested circuit by circuit as you wired them up

Something to tuck away............

When troubleshooting and there is the danger of either an unfused short (wiring smoke/ melt/ damage) or damage such as you are dealing with here (gauges) Wire an APPROPRIATE sized / wattage lamp in series with the battery ground.

The IVR by the way has a ground point (3 terminal) so screwing around bypassing it is a bit dangerous.

If you cannot get a gauge reading by grounding the sender terminal, then check if there is power (As Dana said) in and out of the IVR

Also I WOULD NOT use an OEM style (electro / mechanical) IVR. Buy one such as RTE. They used to be around 50 bucks, but may have gone up