Fuel gauge not working

Didn’t know shit about vehicles a month ago, now dropping a new crate engine this weekend. Learned a lot, anyways I got an 87 Silverado and the fuel gauge didn’t work when it was running, has dual tanks with the tank selector switch. The guy my grandma had work on it did some half ass shit and taped up the wires that run to the switch and made it to where only one gas tank works. Is this causing my issue of the fuel gauge not working? If so how do I get it working right again, as in running off both tanks? I’m gonna check fuses but this is just out of curiosity, idk how he ran it like that.