My early car does not have that style switch. That being said, ideally the wires should be long enough to pull them through the openings, assemble everything on the back of the switch and then push them into place
if there is no apparent free play with the wires, take a small flashlight and a mirror and see if you can follow the harness and possibly gain some slack by opening one of the factory harness positioning straps/clips?
good luck
Larry