i have recently restored a 1986 Oldsmobile delta 88 royale brougham and everything is working, but the fuel gauge sometimes when i turn on the car it will light up and then off and will randomly come back on and when it is on it will say something like i have a full tank when i know i don't have a full tank. or i have a quarter of a tank when i filled up 20 minutes ago. for now i just fill up about every 130 miles but it would be nice to have a working fuel gauge .So what i'm asking is does someone know what is wrong with the gauge and how to fix it

here a video of the gauge