what is the blue connector on the sensor plate for

[Walt Fricke]

1) The AFS plug is a convenient way to allow the fuel pump on these model 911s to run without the engine running, for various testing purposes. Just reach back there and unplug it, plug it back in again when done. With only one of the confusing two plugs in the area undone, you won't inadvertently plug the wrong one in. That often happens when you are reinstalling things after a rebuild, though.

2) The reverse logic fuel pump relay is a tricky devil. I know what it does, though just why that works is something I can sometimes sketch out from memory, and sometimes can't. But it isn't really complicated, and as long as the wiring diagram is followed, works fine.

The AFS switch must be a normally closed switch (relay not activated). It grounds the relay coil in the FP relay, connecting the unfused +12V, which comes from the direct from the battery start position of the ignition and powers the starter, to the fuel pump. When the AFS opens, the FP relay, a NC switch, opens and its other pole connects the fused +12 FP circuit to the battery +.

3) As a friend one pointed out to me, while the "turns fuel pump off in crash when engine dies" function is certainly useful, it won't work if the car is upside down! Gravity should cause the plate to move and open the switch.

4) Short of a short somewhere, I am baffled by the melted wires. I don't doubt Tony's experiment (perhaps inadvertent?) as being what happens with reversing these plugs, but I don't see why it should happen.

Both the CSV and AFS connecting wires are 0.5mm small gauge wires, for one. Assuming the plugs have their + and - sides in the same keyed position, hard to see why that would overload a wire. The CSV and TTS circuit is only connected to +12V with the key in the start position.

Reversing plugs would (?) conduct the FP relay to ground via the CSV heater coil. Thus the relay coil would always be on, but so what? Relay pin 87 is fed by a 1.5mm wire, same as 87a.

4) Other than because Porsche did it, why should the connection of the AFS to ground be only to the alternator ground. Any engine ground should do (a chassis ground should work, too, but with more wiring complication) shouldn't it?