1992 Buick Century power windows

For a four-door, my information shows two grounds coming off the master switch, one for the front windows and one for the rear windows, black wires.

You need to get at the wires coming off the master switch. Just to check for a ground issue, you could use a jumper between the two black wires, try to test close to the master switch. If all the windows work, it's a ground issue.