I cannot say conclusively that you shouldn't hear the fuel pump on all years with the key in the on position, but that is my understanding. Mine is an '83 so I have all the bells and whistles they could do with the CIS system.
If you reach around with you left arm and feel around on the back side of the engine a little bit down and to the left of side of the air box, there is a plug that plugs into the pressure plate sensor. It is a bluish green color. That should be connected. If it is disconnected, the fuel pump will run with the key in the on position.
When my fuel pump runs without the engine being started it is a distinct sound. A loud hum is the best way I can describe it. Here is an old video I did. When I switch on the fuel pump (jumping the connection), you can hear the sound.
Porsche 911 CIS Cold and Warm Control Pressure Test - YouTube
If you don't have a known good relay, just try jumping the pins with a fused circuit for a quick test. I'm not sure if another relay will work. I think the others have a different capacitor.
Like the other guys said, check the pump and relay. If those check out, I think it would be time to get the gauges and work your way through.