I know I can tap in at the coil but I rather stay away from there if at all possible and make a connection closer to the dash via diagnostic connector.
I have to say.. I've been searching myself for 45 minutes and it's surprising how difficult it is to find a good wiring schematic that includes what you are looking for. Somewhere I have an old hard copy chilton book with complete schematics but dang if I can find it either.. ugh! Sorry bud. That's usually when I hit the ol' Stangnet easy button: @jrichker
I know I can tap in at the coil but I rather stay away from there if at all possible and make a connection closer to the dash via diagnostic connector.
There isn't a tach or shift light pickup in the diagnostic connector.
The instrument panel does have the feed for the stock tach, it is a AC pulse that varies in frequency and voltage. The peak voltage is from 10-15 volts. The voltage is not what the tach or shift light uses for information on what to display, it is the frequency that controls what you see on the indicator.
Before using this as a connection point check with the shift light manufacturer. They may need to connect to the TFI side of the ignition coil to work properly.