I have a 2000 Ford F150 that has recently started giving me problems. Everything seemed fine until a week ago. I went out to start the truck and the battery was completely dead. Pulled the battery and installed a brand new fully charged battery. The heater blower motor was running on low speed with no key in the ignition which I assumed was the reason for the dead battery. I started the truck and let it run until warm with the heater blower on high. Everything appeared normal. When I turned the key off, the blower remained on but at about 1/2 the high speed. The only way to shut the blower fan off was to use the directional dash switch. Two days later it worked just fine, ignition off-blower off. Today blower will not shut off with ignition. Is this an ingnition switch problem or is there some type of control module for the heater blower motor. Any suggestions would be appreciated.

 

Welcome to FTE!

Have you checked the fuses/relays in the cab and under the hood. Sounds like a relay may be getting stuck. Just a thought, not really sure. If you have your owners manual, it will tell you which relays are for the blower.

Oh, and don't forget to get your cruise control (if you have it) switch checked out at a dealer before your truck sets itself on fire.....

 

Looking at my '97 diagrams, there are two possibilities. There is a 40a fuse that feeds the Blower Relay power. That fuse if fed from hot at all times. The input to the relay is from a 10a fuse that is only hot when the ignition is on and goes through the floor, panel/floor, panel, flr&def, def switch.

The blower should not run with the ignition off. Since it does, first see if it will run with the flr/pnl/def switch in the off position. If it does, the blower relay is bad. If the fan does not run when in the off position, the ignition switch is faulty.

In either case, a wiring fault like one wire rubbed into another, a short to power, etc. could cause this. Try the test above first (assuming I can still read an electrical logic diagram). If it shows the relay is bad, pull the blower relay. If it still runs, wiring problem, if not replace the relay. If the ignition is always hot, reply back and we'll take a shot at that.

 

Hi gamebird and welcome

Has it been raining much where you are?
A common problem is the windshield leaks water into the fuse box which shorts it out inside. Usually when that happens the heater motor stays on. It can also hurt the GEM (Generic Electronic Module) which is bolted to the back of the fuse box and controls the 4x4, wipers, power windows etc.
The cure is to get the windshield resealed and replace the fuse box and possibly the GEM. You can sometimes wiggle the fuses around and hear arcing inside the fuse box.

 

Thank you all for the welcome and for the information. I will check out the fuses, relays and the ignition switch. No noticeable leak anywhere although a slight amount of snow did come threw a slightly open window. I was a mechanic for 25 years (retired for some time now) and everything has changed, under the hood and electrical. Too many sensors, relays, and computers now. Fifteen years ago it would have been a simple ignition switch change. Now who knows? Hopefully one of the new breed of mechanics. The radio/ CD has a quirk also. It does not turn on for almost 1 minute after key start up when left on. CD player will not take a CD (CD ERROR) message. Any coments about that from anyone???
Thanks again. Will let you know what I find.