Get a 12V test light. Disconnect negative battery cable. Hook test light the negative cable and the negative post of the battery where you removed the cable. If there's a short present, the test light will light up.
Be sure everything electrical is shut off. Doors closed so dome light is off, etc.
Pulling one fuse at a time, check to see if light goes out. You can sometimes isolate the problem circuit like this.
First things to check would be alternator, regulator by unplugging them.