I have a 2002 F150 SCAB. Went to drive it today and the battery was almost completely dead. Jumped it off and ran fine. Truck sat for a couple of hours and then drove it again. When I turned off the the ignition after driving, the heater/AC fan came on. What is happening here? Is this some sort of short in the ignition?

 

Hey WPBronco.
I bet you might have a GEM module going to the bad. It seems some trucks develop a water leak that lets water get into the fuse box and Gem module, which is mounted on top of the fuse box under the dash. I think that there is a fuse for the gem module you can pull and see if all quits.

Dave P.

 

your GEM is on the way out.

 

Just an example of how you can damage electronics from voltage spikes. Obviously, you generated voltage spikes from jumping your battery.