Clutch coil fails immediately even with no power EVER being plugged in.

[bigoilman]

The vehicle the compressor came from has a 2 wire plug.

Inside the clutch is a diode ACROSS the coil windings. Wired properly, it shunts the reverse current from the magnetic field in the clutch when power is removed.

If you ground the wrong wire from the clutch, the first time you energize it - you feed a dead short to ground through the diode. Most of those diodes are only rated 1.5 to 2 amps. When you nail the diode it often fails shorted. Then you have a built in short across the clutch coil.

Your aftermarket plug has a second diode from your description. Is it wired across the two terminals in the plug?

Yes. I wish I could post pics here but it is a black diode with a silver stripe on the positive feed. Although the connector is different, it looks like this and is wired the same way. http://www.casperselectronics.com/cart/ ... uct_id=296[/url]

[bigoilman]

I'll update this thread just in case someone comes across it later.  There were 2 issues:

1. The aftermarket pigtail had a diode crimped into the plug.  The compressor already has a diode built into the clutch. Another one isn't necessary and is a potential problem.
2. The REAL culprit....The damned aftermarket pigtail was wired BACKWARD!!!!  Never picked up on it, even with my test harness because the device I had connected to it (air pump) isn't polarity sensitive other than reversing polarity makes it change direction.
I finally caught it this morning when I borrowed a crapped out compressor from my A/C guys scrap pile that had a good clutch.  Brought it home, spliced the pigtail from one of my 2 dead compressors on it and when I went to marry the two halves of the connection, the wires were opposite!  Repinned the connector and tested it multiple times and the clutch engages from my dash switch EVERY SINGLE TIME.

Thanks for all that responded.  If this isn't the final solution, I'll update.  Otherwise, this was the problem and CASE CLOSED.