Fluctuating Unsteady gas gauge

I finished installing a new fuel pump in my gas tank this evening. Started it up to check everything out. Fired right up. But my Gas gauge went to Full, then crept bck to half full, then back n fourth, then to full again. I know theres just Under a quarter tank . What could possibl cause the gas gauge to do this? If the fuel sending unit were bent during instal ,it would just read a wrong reading maybe,right? Theres only one wire (purple) going to the fuel sending unit .cant be crossed wires. wow this ones freakin my brain out. Wish the gauge would just say somewhere.

You have a loose wire somewhere. It is grounding out before it gets to the sending unit.

Back by the fuel tank...theres one pigtail connector that has 3 wires. Black is ground and orang-ish runs the pump & purple goes to the sender. I havent done anything else.This is quite puzzling.I cant imagine what could be grounding out cuz theres just one ground wire & thats securely mounted to the outter base of the fuel pump. hmm weird. well, ty im gonna sleep on this one. cuz im utterly confuzed & tired from working on that truck all day.

just to update: For the first 5 minutes after fuel pump was replaced ...my my Gauge was flipping out & unreliable. Next moring (yesterday) I drove to town And back & the whole time ,the gauge appeared to read right. On the way up town it read 1/8th ...I put 10 bux in and it went to just barely above a 1/4 about 5 miles later it was on a 1/4 ....seems right to me.