You won't read any voltages on the wires going to the hazzard switch, except on the Blue/White one when the hazzards are working. The flasher relay does all the magic. You just have to ground the Yellow/Purple wire to get hazzards. Most likely your switch is corroded as others have pointed out and you'll need to clean it, also as others have pointed out. If you want to verify that you have operational hazzard lights, ground the Yellow/Purple wire after undoing the connector. With the ignition on, you should get 4-way blinkers as long as the wire is grounded.