Where is the window relay on a 1965 Ford Thunderbird?

There isn't a single, dedicated "window relay" in the way modern cars have them. 1965 Ford Thunderbirds used a simpler system. The window motor operation is controlled directly by the switch, through the wiring harness, with no intermediate relay. Any problems with the window operation would typically point to issues within the switch itself, the motor, or the wiring between them.