Blower motor failing

[Woodhook13]

I’m restoring my 77 k10 and have installed a new wiring harness.  Also bought a new heat/A/C fan switch.  My blower motor comes on when the ignition is turned on, which is normal.  I have 3 fan speeds that work perfectly but when I put the fan to high, I blow the fuse in the fuse panel marked heat/AC.  If I unplug the relay (which is new) the fuse doesn’t blow. Of course the fan doesn’t come on either.  I have ohmed the orange wire back to the switch and it is ok.  I’ve also put voltage on the orange wire to make sure it wasn’t grounded out somewhere.  I do have ignition voltage on the red wire coming to the relay.  The blower motor works fine if I connect it straight to the battery, which is high speed.  I’m going to test the relay this weekend to see if I hear the switch operating.  I don’t think the high speed goes through the resistor, but I did take it out and it looks fine. Am I missing another spot that I need to check?  Could the new relay be shorted out causing the problem?  Any suggestions would be greatly appreciated! 

[Mr Diesel]

Sounds about right. I would throw in a new motor. They are cheap.

[bd]

I’m restoring my 77 k10 and have installed a new wiring harness.  Also bought a new heat/A/C fan switch.  My blower motor comes on when the ignition is turned on, which is normal.  I have 3 fan speeds that work perfectly but when I put the fan to high, I blow the fuse in the fuse panel marked heat/AC.  If I unplug the relay (which is new) the fuse doesn’t blow. Of course the fan doesn’t come on either.  I have ohmed the orange wire back to the switch and it is ok.  I’ve also put voltage on the orange wire to make sure it wasn’t grounded out somewhere.  I do have ignition voltage on the red wire coming to the relay.  The blower motor works fine if I connect it straight to the battery, which is high speed.  I’m going to test the relay this weekend to see if I hear the switch operating.  I don’t think the high speed goes through the resistor, but I did take it out and it looks fine. Am I missing another spot that I need to check?  Could the new relay be shorted out causing the problem?  Any suggestions would be greatly appreciated!

Blower Motor Relay (Keeps Blowing Fuses)  -  Read it all the way through to the end.

[Woodhook13]

Thanks bd!  I’ll try a new relay with that diode cut out!  I’ll post my results when I’m finished!

[bd]

Or, you might save yourself some time and money by reversing the positions of the orange (+) and black (-) relay control wires in the two-wire relay connector, so that the diode won't 'fry' anymore.