Does anyone know what voltage I should be getting to the PVHS? There are 3 wires going to it. With 4WD off I get 12v to the middle pin. When I turn on 4WD the voltage stays the same on the middle pin. I'm trying to decide if I need to replace it or not.

 

There is always voltage to pin 2 with the key on. Pin 1 is grounded to lock the hubs, pin 3 is grounded to unlock the hubs. Vacuum is applied to the hub for only about 15 seconds. A stronger vacuum pulse is used to lock the hubs and a weaker one to unlock them.