so if the gas and temp gauges don't work...

67Dart273 said

The original IVR works like a signal flasher. It pulses (breaks) 12V up into approximately a 50% duty cycle pulse, so effectively about half

Some modern replacements are a 5V DC regulator

So if you had an original working IVR, you would see a pulsing voltage on the sender wire, not necessarily 5V

Click to expand...

I see... does it sound like IVR to you? (again, there's absolutely no reaction in either gas or temp gauge when the key is turned-most of the search results I found mentioned the gauges pegging when the IVR went).
If it's a bad connection like you mentioned earlier, is there something else I'd notice? The gauge lights are working, but I don't know if that's a different circuit...