No Power to Blower Motor

[Gary from Texas]

So I'm troubleshooting an issues with my 91 Comanche.  The blower motor stopped working.  I have 12V getting to the motor when it's disconnected, but as soon as I connect the motor it goes to 0V.  I have bypassed the blower resistor, the blower speed switch and the HVAC selector switch.  The problem appears to be between the 25 A blower fuse and the input to the selector switch (the pair of black/tan wires).  I see the 12V at the end of the connector and it goes away when I pull the fuse. But I don't have continuity between the two points.  I show 37K ohms of resistance.  My question is, are there any other components between the fuse and the selector switch or any place else I can test this without having to pull out the fuse panel?

[pizzaman09]

Are you confident that your blower motor works?  In my experience blower motor problems are either worn motor brushes or a bad fan speed selector switch.

[Gary from Texas]

I did check the blower motor by connecting the 12v line to the battery and using the same ground. Seemed to work just fine. 

[cruiser54]

Anything else not working? Like radio and turn signals? 

[Gary from Texas]

Everything else on the truck is working correctly. 

[Eagle]

There's a link to the factory electrical manual floating around here somewhere.

 

Your post wasn't clear. Do you have 12 volts at the input side of the selector switch?

 

[Gary from Texas]

I do have 12V at the selector switch, but it goes to 0V as soon as I connect the blower motor.  This happens even if I bypass the the entire control module and the resistor. At this point, I think I have to pull the fuse panel and look for the problem. Not looking forward to that. 

[Ωhm]

You might want to use a simple 12vdc testlamp for trouble shooting this problem. Voltmeters (high impedance) will show/display 12vdc while a testlamp (low impedance) will not light or light dimly.

[zomeizter]

12v going to 0v under load is an indication of high resistance, check every connection point to include the fuse and sockets, that's where mine had a bad connection. I solved this by cleaning the sockets in the fuse block with contact cleaner and the blades on the fuses with fine sand paper or Scotchbrite pads.

[gogmorgo]

Where is your ground when checking for 12V? Did you try jumping power to the blower motor to see if it comes on?

[Gary from Texas]

My volt meter is grounded at the metal frame under the dash. I used the existing ground wire when testing the blower motor with 12V connected to the battery. 

It's freezing cold out this week, so further testing will have to wait until the weekend. 

Has anyone taken apart a fuse panel? Are there any risks of something going wrong and not getting it back together.  I know about the hidden bolt in the engine compartment, but otherwise it looks pretty straightforward. Wish me luck. 

[Gary from Texas]

So for anyone following this post, here is the final result.  I attempted to remove the fuse panel to find the issue with the wiring.  I took out the 2 screw under the dash and the one screw from the engine side (very difficult), but I wasn't able to get the two halves apart.  I'm guessing it was weather sealed and I didn't want to mess with that.

Anyway, I ended up putting in an 'Add a Circuit' into the fuse panel and running a new wire to the HVAC control.  Everything works great now.  Thanks for all the help.