Ported vacuum allows you to set the initial timing without disconnecting the vacuum line, unless you've got the idle speed set high enough to expose the port. The vacuum signal should begin just off idle, and increase with engine speed. On acceleration, hill pulling, or trailer towing, the ported vacuum goes away and you're back to straight centrifugal advance like the original distributor works. The power wire from the ignition switch to the cap needs to be at least a #12- - - -#10 is better. The tach wire is optional, but that's where it gets its signal if you've got an electronic tach.
A hidden toggle switch connected to ground and that tach terminal makes a great anti-theft device.
Jerry
