I have a 1999 f-250 7.3 6 speed and my blower motor stopped working on all speeds. I put a new blower motor resistor on it and a new fan speed switch in the dash with no change. My fuse 22 under the dash is good and I’m getting power to both sides of it. My 40 amp fuse under the hood is also good and I have power to both sides of it. I swapped the relay, 2nd from the firewall, with a known good one from my other pickup with no change as well.

with the fan switch on and the selector switch for the defrost/vents on I have power at the blower motor on 1 wire. I think it’s brown/orange. If I run jumper wires from the battery positive and negative to the blower motor terminals it will run. After I jumped the blower I re installed everything and the blower worked for a couple seconds before it quit again. With a test light I show to have no power to any of the resistor terminals or to any terminals on the plug in on the speed selector switch. (Not sure where there should be power if any)

Is this a ground problem? Does anyone have an idea of something I’ve overlooked or could try to fix my problem? Thank you for any/all help and suggestions. -Ryan

 

You're well on your way. Here's the roadmap (schematic) that should guide you the rest of the way.

There should be power on the O/BK wire at both the resistor and the speed switch. Since you had power at the BN/O wire at the motor but none "downstream (per your report), I'd assume that either the blower motor is bad or the O/BK wire has an open circuit (bad connection, etc). You can install a grounding jumper to the motor's negative terminal (positive stays connected) to verify it it's the motor or if it's the rest of the ground side circuit. If the motor is good, it will run at full/high speed.

 

I have see the hot wire at the motor lose contact before. Wiggle it around to be sure.

 

I have a similar issue but strangely enough once I hit a couple of bumps it comes on. Once I figure out why it smells like diesel fuel when the air is on I will tackle that mess haha.

 

Thank you all very much for the replies. It’s been too cold to work on it the past couple days but as soon as it warms up a little I will do more troubleshooting. Your help is appreciated!

 

Wanted to thank everyone for the help and ideas. I got it fixed today. The pins in the electrical connector on the blower motor would wiggle around and not make good contact. Every now and then when everything was just right it would work for a few seconds but then would quit. That even was the same case when trying to jump it straight off the battery. I put a new blower motor in it and it came with a wiring pigtail and all is well now! Hope this can help someone else in the future. Thanks for the help!-Ryan