Any time I've "tested" gauges, I used a 6v lantern battery and tested for needle movement individually. I've never tested with 12 v and thru ivr/fuel gauge.
I'm an idiot when it comes to elec.voodoo(and more lol)
@67Dart273 ,
@RedFish and
@Mattax @moparmat2000
Can help you out. Just my opinion, BUT you've gone this far....use an external VR and clip the internal one. 55 years old. Its had a good life lol.