Installing an MSD-6A in a 1972 Mustang

I'm installing an MSD-6A in a 1972 Ford Mustang, 351C-4V, manual
4-speed toploader. I need to connect the small red wire from the 6A to
a +12V switched source (needs to be +12V at the run and start
conditions of the ignition switch). Any recommendations as to where to
tap in for this source? On the starter relay, there one of the small
posts is +12V in the run, but I don't know if it is +12V in the start
position.

Thanks...