Fuel Pump Sensor Plate Switch

I've read that the fuel pump should only operate when the car is running, or being started. My fuel pump runs constantly with the ignition in the "ON" position. As the CIS is completely apart, I looked closely at the sensor plate housing, and noted a light blue connector on the back of the housing.

The thing is, I don't see how this system operates. I realize it activiates when the sensor plate rises (with the engine being started or running), but there are no holes, switches, or anything else that indicates how this system works. The PO had this connector removed, but I'd like to get it working to factory specs before the engine goes back in the car. A while back, I hooked the connector back up before the engine came out of the car, but the fuel pump still ran with the ingnition switch in the "ON" position.

Can anyone let me know how this system works? Is it a magnetic sensor of sorts?

Thanks!

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Michael
'78 911SC Euro

Michael, according to Bentley, this is the sequence of operation:
"During engine cranking, the fuel pump is supplied power from Terminal 50 of the ignition switch (hot in start position) through the fuel pump relay. Incoming air then causes the air flow sensor plate to lift and open the sensor plate contact.
This de-energizes the fuel pump relay coil and routes Terminal 15 power of the ignition switch (hot in run position) directly to the pump."

Hope this helps you.

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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

Thanks...does it show where the sensor plate contact is?

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Michael
'78 911SC Euro

As the Mixture Control Unit sits installed on the motor, the plug connector is at the rear and underside of the intake venturi. It's a little plastic do-dad that takes a plug-in.

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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

If you are looking for a "switch", there isn't any. At it's rest position, the sensor plate grounds against it's stop and interrupts the fuel pump circuit. When the sensor plate lifts off of it's stop by air flow from a cranking or running engine, the sensor plate breaks the circuit and causes the fuel pump to operate. Look closely at how the connector is mounted. A little testing with an ohm meter and you can figure out how it works.
Bob W.