The door locks run off a circuit breaker on the starter solenoid.
You failed to indicate what year car this is. That makes it difficult to insure that you get the right information the first time. Once you have updated you signature, I will post the correct diagram for your radio power problem.
To update your signature, hover over your user name on the top RH side of the page. An information box will appear below your user name. Click on Signature and then fill in or edit it to include information about your 5.0 Mustang. Things like the model year, body style, modifications to the car go in there along with any suitable comments.