I have a 2001 LS Blazer. Strange problem started recently after a heavy rain, maybe this was just a coincidence, but my dome lights are on all the time. Have to use the overide to keep them off. The security light is flashing when the key is off, not when running. The radio is on but no sound. Sometimes if I play with the power door lock switch enough times the radio will play for a second or two then quit. I've torn apart all the door panels and the tailgate but don't see anything obvious. Completely stumped. Hope someone can give me advise on where to look.

 

You can do a test by hooking up a tester to the battery to see if theres any drain by doing a parasitic draw test. If the dome light is on with the key off, then this test will show it on the dc amp side . You can pull each fuse and relay to find out where to start.
youtube - parasitic draw test