Steve may be right, although the wiring diagram for a 78/79 still show the safety switch, and the position is on the throttle body housing. Kind of suggests to me that if the throttle plate opens too far, the safety switch signals the fuel pump relay to shut off the pump. That's what I think is going on. The wiring diagram shows the 2 pins you mentioned going to the safety switch, but this is 78/79. On an 80, pin 4 is the rpm input to the relay (which is how they started protecting the engine in 1980, instead of the safety switch) and pin 5 is ground for the fuel pump relay and also the same ground is used for the ground for the Lambda voltage supply relay.
I'm more convinced now that the info you have is for 1979 and earlier and you should discontinue referring to it.