Yeah, had a feeling that would solve it. Nothing is coincidental, cause and effect. If you don't like the effect, reverse the cause.

Good luck on future endeavors

 

Well why am I not surprised..

The Series II Fuel Gauge in cluster is not 'in-accurate' or 'poor', you were getting wrong readings because the S2's uses different Fuel Tank Sender units (2) to the ones used in Series 1.

Series 2 has a larger Fuel Tank also, hence the different Tank Gauges, hence wrong reading, running out of gas.

But thanks for going where no one has gone before...

Edit:
Here is a close up pic of one of the two Series II Fuel Tank Gauges, all fuel tank gauges work by supplying a very low milliamp voltage back to dash cluster, each increment (contact) on circuit board via the float has a different output.

 

Thank you! I really appreciate the comments, pics, and insight

 

Dimming could also be a culprit of a bad ground connection. I had this problem for a little while, and I remember backing into to my driveway slowly letting out the clutch without giving gas. When the rpm's dippped a little under idle my lights used to dim. Double checked, and turns out my negative cable on the battery was left a little loose lol. Tightened it back up and no more dimming.

 

OP already figure out the problem, and it was far more complex than a bad ground, read the thread next time.

 

Thread closed, the problem was the OP installing a Series 2 Dash Meter Cluster in a Series 1.