Ignition wires

So I know to hook the small red msd wire to a switched 12v. From what I've read alot of people splice it into either the IGN 1 or IGN2 wire. And looking at the wiring schematic I can't find which wires they are.

I'd like to tie it in under the dash not in the engine compartment.
Thanks

So what year / make / model are we working on, and what schematic are you looking at?