See that's what I'm saying makes no sense.
Whether it was by installing a resistor or getting resistance through the sender, 10 ohms should have had the same result on the gage with the engine running.
Could be a poor connection either at the attaching terminal or in the ground.
Yes you could bench test the gages (and the IVR) with the instrument panel out and connected to a battery.
IVR causing a fire??? AFAIK only if they've been messed with. Search for Redfish's posts about safe and less safe ways people repair, modify and disable.