A lot of my electrics work a lot better after I put a new ignition switch in, after it went dead snd wouldn’t even turn over. My fuel gauge was all over the place like you are saying, and my rear no. Plate light never worked. A new switched fixed it all.
My fuel gauge regulator had burned contacts and the aveeage voltage dropped off as well as the sender wearing out. Made it all a bit random . I peeled the regulator apart, cleaned the contacts then reassembled and adjusted it.