heater blower motor not working

[sethkitchen73]

1968 Ford F100 truck. 360 V8 with Automatic Trans. No A/C.
my heater blower motor quit working. Its been sporadic over the last year but finally quit all together.
I have read 13 - 14 on my electrical meter with engine on at the tip of the BROWN that comes from the Resistor found behind the metal fan housing. This BROWN wire is the power source for the blower motor (fan). With the BROWN wire from Resistor connected to the ORANGE wire on the Blower motor, I then connect the ground wire. As soon as the ground wire touches the metal where it will be connected it SPARKS, the blower motor turns on for half a second then stops. It has blown the 20A fuse when I have tried this before.
I have replaced the ignition switch and wiring pigtail.
I have power at both sides of the Heater Fuse.
I have power all the way to the point of connection at the variable speed switch for the heater
I have power to and through the Resistor
All gauges, lights, radio, etc...work

Is this a ground issue??
Thanks,
Seth

[68RGR]

Have you tried removing the fan motor to see if it binds when the shaft is turned by hand?

If not, give that a try - It should turn fairly freely and quietly.

Regardless, it could be a bad fan motor. Blowing the 20 amp fuse means a whole lotta current is being drawn. If the motor has failed electrically, that could explain all of what you are seeing. If you have another small, 12 volt motor, connect it in place of the fan motor and see what happens. If it runs well, you probably need a new motor.

[1972hiboy]

Seth. your post seems like its missing a few words and using words that dont belong, autocorrect maybe? First off welcome to fordification I see this is your first post, please make sure you head over to the welcome mat and introduce yourself to everybody. When im checking blower motors I like to unplug the blower motor completely from the van/truck and hook my power probe up to the blower and apply power to it. If it turns on I at least know the motor isnt seized and it may be a control problem. This leaves you with the switch wiring blower motor resistor or fuse, usually if the motor is good ill check for power right at the blower motor plug and see if im getting a power signal from there. then work my way back to the dash.

[sethkitchen73]

Thanks guys for the response. I tested the blower motor by directly touching it to the positive and negative terminals of the battery, it works fine. This makes absolutely no sense.
Previously, with the help of my father in law, I could get the fan to come on by wiggling the wires behind the ignition switch but only briefly. Thats why I replaced the ignition switch and wires behind, I thought the issue was there. But now with new wires I still have the same problem.
I had a buddy look at it, he has an electrical meter with a small lcd screen and a built in fuse. When he touches the brown (power) wire that comes off the resistor and then touches the ground to the truck, it blows the internal fuse in his electrical meter, "pops the breaker" so to speak.
The original wiring pigtail from the ignition had slightly melted where the yellow power wire was connected.

What are the symptoms of a faulty resistor?
Seth

[68RGR]

The resistor module is just two coils of wire that form two small-value resistors. The larger value is the low speed, the lower value is the middle speed and, when neither of them is in the circuit, you get high speed. If something related to it has failed and is touching ground, that could explain what you are seeing.

How about trying this - Disconnect both motor wires from the truck. Using an ohm meter, measure the resistance between each wire and the CASE of the motor. I'm thinking you should see infinite resistance between the positive power wire (I think you said it was orange) and the case of the motor - In other words, there should be no connection at all. Of course, if the negative wire (the ground wire coming off the motor) is connected to the motor case internally, then this test won't work. You'll know that is the case if the resistance between the ground wire and the motor case is close to zero.

Somewhere, you have a short to ground. Otherwise, the fuse wouldn't be blowing. It could be in the wiring, at the resistor, inside the motor, etc. The yellow wire being melted at the ignition switch indicates that too much current was flowing through it at some point. Is it possible that you didn't find all of the wires that were damaged by the heat? The wire (black with yellow stripe on my truck) that comes from the battery to the ignition switch runs almost the entire width of the dash. If it overheated, it could have affected other wires that were touching it. I put a circuit breaker in the black/yellow wire under the hood in an effort to keep the wire from burning up due to ignition switch or other problems. See http://www.fordification.com/forum/view ... =8&t=70768

[sethkitchen73]

Thanks, I'll give it a try a get back with you.

[sethkitchen73]

So we figured it out!!! The resistor was grounding itself on the metal blower motor housing. I rebuilt the plastic piece used to attach the resistor to the housing and modified the rectangular opening that the resistor slides into so that it would not rub or touch the sides. It now works just fine....Thanks for all the suggestions and help.
Seth

[1972hiboy]

thanks for posting the repair solution. and good to hear its working now!