I can see that useful when your overall resistance is wrong.

ie a 29 to 91 resistance vs the 10-80 you need. mismatched sending unit to gauge.

but the issue I keep seeing is that it doesn't read right through part of the travel. As mentioned above. It reads full. but doesn't transition correctly and suddenly you are at half a tank. and it suddenly goes to empty.
I don't see this helping with that, as it would be a variable resistance problem though the travel.

I can see that useful when your overall resistance is wrong.

ie a 29 to 91 resistance vs the 10-80 you need. mismatched sending unit to gauge.

but the issue I keep seeing is that it doesn't read right through part of the travel. As mentioned above. It reads full. but doesn't transition correctly and suddenly you are at half a tank. and it suddenly goes to empty.
I don't see this helping with that, as it would be a variable resistance problem though the travel.

Daylight driving the gauges work fine. Turn the headlights on and the fuel,oil pressure, and gas gauge drop to zero.

To me it sounds like the gauge voltage limiter is losing a ground or voltage. If they work ok without the headlights on and go bad with the lights on the power or ground seems like the problem. Try running an extra ground to the cluster.

Sometimes you dont get a good ground from tank to frame. Did you put the ground jumper across the hose from fuel line to tank ? Take an alligator to tank lip and then to frame. Make sure you get good grounds see what happens and let me know. good luck

Potentially cool little widget but strikes me as pretty pointless. I don't find it difficult beyond reason to calibrate a tank sender on the bench. Clean the reostat contacts, bend float arm, resolder connections, test with an ohm meter. As long as it reads empty before it's actually empty, I'm good.