How to wire aftermarket radio in 66 Barracuda?

If the factory radio wiring is still there you'll find a connector with a red wire and a orange wire. red is switched power from the radio fuse. Orange was for a dial lamp that was poked into the radio. you likely wont use that for a aftermarket unit. As for constant/memory power... cig' lighter is one always hot source. Do fuse the memory wire though. There's 20 amps available most anywhere you do tap a hot wire. Thats a heck of a lot more juice than req'd for a memory circuit.