I hear a fan running when my ignition is off and it's killing my battery what is the cause of this problem?
That is probably the engine cooling fan. It should shut off after a couple of minutes but if it does not it would run your battery down. Is your battery weak or does the fan keep running?
What F_O_R said all so check the coolant fan relay,may be stuck.
If your electric fan is running your battery down you may already have a problem with your battery taking or receiving a charge.
Looking for a Used F-150 in your area?
CarGurus has 203,183 nationwide F-150 listings starting at $1,273.
Search Ford F-150 Questions
Ford F-150 Experts