1985 Other Toyota Models gas gauge

first you got to see if the wiring harness and the guage is good or if it is a issue with the harness, guage, sending unit.

to do this disconnect fuel pump signal line from the sending unit and ground it out, does it show empty? put on +12v does it show full if not the harness is damaged or the guage is no good.

if it functions properly check the sending unit.