Heard a loud pop under the dash behind the radio. Lost power to head lights, all running lights. Thought lost serpentine belt but didn't. Battery was completely dead, put in new alternator and obviously have a short ( am guessing the loud pop was the culprit, to what I do not know) Now, the running lights "stay on" when the ignition is "off". IF the battery cables are not disconnected from the battery in will be dead over night. Turn headlights on it blows the fuse to all lighting, headlights, turn signals, etc. Found a solid brown wire that goes to the light switch and using the test light has power to it at all times when ignition key is in off position and the head light switch is also in the off position.

 

First things first, disconnect the battery, get a good flashlight, and get under the dash.
Start looking for scorched wires, anything that shows bare wire, burn marks. Also first thing I always do is unplug the back of the cigarette lighter when stuff like this happens, those damn things always gave me trouble.

Try disconnecting that switch- The brown wire runs to the back of the truck, it is what powers all lights in the rear it is the positive side to all those lights.

 

 

Bad headlight switch.