fuel gauges

Long story short I swap 90 Integra cluster for a 92 cluster and then swap back to my original stock cluster. Since I put my original cluster back on the fuel gauge light lit up. I know there nothing with wrong with my cluster so what could make the light turn on?

Drum roll, almost out of gas?..sorry, I could not resist. I had this happen with a family friend he thought he needed a fuel pump… Just needed some gas in the tank.

Ya know now I re-read this yes I have had this happen when mine is like 1/3 or 1/2 full sometimes but usually when I get to my destination it shuts off but I swapped a 92-93 Gsr cluster in my 90 so I have personally noticed this but either way only has happend a few times since I got my car running