Note that some stupid CD players consume up to 0.14A in sleep mode. That means dead batt if parked for weeks... (Two pwr supply wires, one for mem settings, one run-pwr via ign key ...is one indication. Manuals were ashamed of warning about pwr consumption.)
Ol radio was connected directly, no need for key to get player on. My new USB player one cannot be, or batt will die: to listen, always ign key has to be turned.
Good ground is also found on the surroundin dash metal structure.