Blower motor not working

I have a 1991 Isuzu pickup, 80,000 mi.
The blower motor does not work.

* I pulled the motor out, and connected it to a 12V source, and it works.
(it is a bit sluggish, so it may need to be replaced anyway)
* If I move the fan switch to one of the on positions, the AC will activate
(shows that the switch is good?)
* a voltmeter across the plug to the motor shows no voltage
* I also do not get a ground continuity at the plug to the motor
(assuming blue w/black stripe is ground, blue w/white stripe +12)

* bad wiring or relay?