Hey guys...I've been fixing everything else on this thing thought my next project needs to be some heat for Winter.
Fan used to work but made a funny noise on any setting higher than one. Then one day it just did not work at all.
All fuses look good and I checked the ground wire on firewall.
What would be a good starting point to fix it?
Relay, resistor or just motor itself?
Thanks!\

73 F100 360 AT 2WD (no AC)

(just hooked it directly to battery for a second and the motor worked)

 

Okay I think I've narrowed it down to either
BM resistor or just the switch itself.
Any way of testing that resistor?
It looks like a grouping of small
wire coils only.

 

Check and make sure the terminals on the switch and resistor are clean and free of corrosion.
Generally, the reason the resistor goes bad is one of the little coils breaks and this can be checked visually. But usually when the resistor goes bad you still have high speed.
See if you have voltage going to the resistor. If you don't have voltage, check to see if you have voltage at the switch.

 

will borrow a meter and check tommorow
hope it's just the switch gone bad,
it feels real loose and sloppy.
Thanks mikeoOoOoO

 

If the motor was making a funny noise I'd run a wire right from the battery to the motor first to make sure it didn't burn up.

 

He mentions having already done that and it worked.

 

yeah I did that as an EDIT and it
was at bottom of my OP, easy to miss
when those ads are there.

Any way to just bypass the factory switch
and tap into the resistor with another
external switch?
Thanks

 

Well I tried just popping in new fuse
and Bingo! it worked.
I had looked at the fuse that was in
it and it did not look blown?
Defrost air not coming thru dash vents
that good but I'll track that down.
THX

 

Hard to see a blown fuse sometimes lucky you

 

That motor starting to drag, drawing more current could very well be why the fuse blew.

 

Or possibly a stick or debris got caught in it.
I pulled alot of leaves and helicopters out of there!
I learned a lesson on checking fuses by sight.
We'll see if it blows again.

 

I just took care of this on my truck - under the dash where the heater box connects to the defrost duct had about a 1" gap where they meet and all the air was just blowing up under the dash. I fixed the alignment and used duct tape to go all around the connection and seal it. I'm getting much better air at the defrost but it still seems fairly week (but I might just be used to new vehicles).