Using Tach w/out the CDI

[911s]

I am trying to find out how to use the factory tachometer to monitor engine RPM without the use of the CD unit. Normally the tach connects to the CDI, and I would like to be able to use it while using another ignition source.

I know with VWs the tach connects to the coil, but this is for an aftermarket tachometer. I'm wondering if I can do the same by connecting the factory tach to an aftermarket coil with provision for a tach connection.

Please let me know what you think. Thanks, Bob (911s).