Fan motor quit working

My heater blower quit working. All speeds low to
high.  I unplug the wiring harness and put my volt
meter on the terminals and I read around 14 volts
DC. Changing from low to high speed it still reads
14 volts. I pull the motor out and connect it to a 12
volt battery and it runs fine. Put it back in and even
though 14 volts is present it does nothing. WTF? I
read somewhere that if the battery or charging
system isn't what it should be the computer shuts
down any modules that aren't necessary for engine
operation. Maybe I read 14 volts with no load. Once
the motor is powered up the computer sees the
draw and powers down the module? Anyone ever
heard of this?