Hello every one,
my 97 F150 has an intermittent but extremely annoying problem. Sometimes when I turn the key off the heater fan doesn't shut off. Most of the time I don't notice when I shut the truck off and I have a dead battery in next day. This might happen once a week or as little as once every 2 months.

When I first noticed this was happening I thought it had something to do with the after market remote start so I completely removed it and I thought it fixed the problem. but the other day when I went out to get in my truck the thing was dead again. Anyone have any ideas?

 

Hello and Welcome!

Sounds like you have a bad switch. Let's see what the rest say.

 

Does the problem happen more when it's rainy?
The most common cause of it is water in the fuse box under the dash. The water shorts across terminals in the fuse box causing the heater blower motor to have power to it when the truck is off. Usually the water comes from a leaking windshield.
The cure is to have the windshield resealed at a glass or body shop and to replace the fuse box.

 

Thanks for the info! I'll check that out

 

I agree, it's probably the fuse block and gem module. Look on the back side and try to see if you can see any green corrosion on the fuse block.