This has been to dealer kept for two days and couldn't figure out. They thought may have been battery, GEM or battery saver relays. I replaced all recommended: GEM had no water issues, battery saver relay and battery, but still same problem sets various amount of time, Can be short as 6-7 hours or may go several days and be OK, generally if sets overnight won't start, battery low and need to charge or jump.

Cars & Trucks - Ford - F-150 - 2002 Ford F150 Regular Cab