Run the "memory" wire to the cig terminal on the fuse box..I'm assuming from what you said the guy with the 70 don't smoke
so you can use the cig terminal...this one is straight wired no fuse (fuse on stereo), and this maintains the memory. On Sony the yellow wire is the "memory" wire, and the red is the "power" wire. the red wire should go straight to the radio terminal on the fuse box. the acc on the ignition switch runs off a different wire, not off of the pink ignition wire, that is why it doesn't turn on your stereo.
run the "power" to the original radio terminal, use female spade connectors. It should work fine. No need to splice up the ignition wire