I have a 2003 Silverado 1500 with 5.3L. A few weeks ago the engine would crank with the key in the ON position. Then a few days later the engine would not shut off with the key off and out of the ignition. I replaced the ignition switch and it worked fine for about 2 weeks then the same thing happened again. Replaced the switch again and it worked 2 days then the battery was dead in the morning. I then noticed that when I hook up the battery, the fuel pump and injectors start and the throttle body makes noise. Just like when you turn the key to RUN even though the key is off. I removed the ignition switch and same thing. The power distribution box is powering everything on with the key off. I switched relays around and still the same thing. I unhooked every plug around the power distribution box and no change. If I pull the PCM fuses the injectors don't power up and I have to pull the IPC/DIC fuse for the fuel pump to not prime in the tank. I checked the grounds and they all seem to be okay. I did find a mouse nest under the side of the power distribution box but I did not find any chewed wires. There was evidence of the mouse being on top of the fuses but no nest up there. Could the fuse panel have a short in it causing this? Anyone have ideas? Thanks.