A friend of mine has a 2002 Ram that did the same thing. We shut the truck off and took the keys out the ignition and tested the fuse box with a tester and ALL of the fuses were showing power!!! Not just the ones that should be (i.e. headlights). To fix it, we just added a battery disconnect switch to the positive battery cable. It's the same one I use on my Nova, it has the big red T handle key that you can take with you so nobody can gank your ****...