One of our dealers, Stable Energies, has done this installation a couple of times on Porsche 997s and was gracious enough to share their secret. We have not independently verified this information so all disclaimers apply.
To connect a tach signal on a Porsche 997:
Locate the ECU box on the interior of the car behind the rear passenger/cargo area under the window and between the shock towers.
Locate Connector E on the passenger (lefthand drive) side of the ECU box.
Locate Pin 6 on Connector E. It should be a Green wire with Blue tracer
Tap that wire and run to RPM input on TraqTach, TraqData, or TraqSync devices
For TraqData or old model TraqTach (grey plastic), you will need the COIL type of device.
For TraqSync or new model TraqTach (black plastic) you will need to flip the tiny switch inside the black cover of the connector from E to C. (It comes set to E)
Set the Car information using Traqview or TraqStudio to CYLINDERS = 1.
Fire up the car and check the RPM in the lower left corner of the Other Features / Check Inputs screen. It should match the factory tach.