The push/pull cable might go to the control valve which cuts the flow of coolant to the heater core.
My heater was devoid of wiring, so I just ran a feed off the ignition through a 20A fuse, and to the fan switch (this is a 12v conversion, I have no clue what the stock heater's resistance threshhold is). I'm sure there are 'bolters who can give you an idea of the factory wiring configuration.
