Tachometer Signal

[surfpac]

Hey guys,
I haven't posted here in ages and I tried searching to no avail. Does anyone know here the tachometer gets the RPM signal from? Directly from the ECU, or through another wiring from the CAS, or coils?
How does it work? is it a digital signal?
Will it work through a PCI bus independent of the ECU?
Sorry for all the questions.

[SpecJ]

Comes from the coil. If you want to get a good tach reading you needs to get a distributorless tach driver. They are about 60-80bucks from our supporting vendors

[Exhaust Depot]

The RPM signal is multiplexed on a wire that also has speed info also. This comes off the ECU. YOu need a tach driver p/n 8913 from MSD. AGP sells them.

[L0c0]

if your looking to use a shift light then yes a tach driver, however if you need it for say an Alarm/autostart, you can tap into the gry/blk (pin 3) wire coming off the ignition coil.

See Diagram