working on a 68 cuda with stock wiring harness.looking for a live that is energized with the key on and key start position.cant seem to find one?

there should be aonly one wire is energized in the start position, it goes to the coil side of the rignition resitor to provide 12 volts to the coil when the starter is engaged, it is either brown or blue, CRS disease I have a 1969 FSM, not a 1968, that i can look that underhodd schematic up and tell you what color it is in 1969 I'm pretty sure there the same colors form 1962 and later for the B bodys
BTW, are you looking for a spare ircuit to use for some other purpose? If so I may not be able to help on that, sorry

With the factory ignition there is none. You'd have to go to an aftermarket ignition that doesn't need the ballast.

I am trying to hook up a msd style box

On the older wiring like you have there is a Start hot wire??? Brown maybe, and a Run hot wire, "Blue" Just tie those Two together coming off the firewall to have a Hot in Both positions.

Yep. Eliminate the ballast and tie the wires on both sides of the ballast together and use that as a power source for the small red wire on the MSD box.

got it thanks