I have a 68 cutlass with transplanted 455 from a 71 delta. The 68 had an external regulator and I assumed the 71 was the same way since the wiring matched up. So why is my alternator sparking? When I'm sitting in the drivers seat with the car running and hood open, I can see arcs at the rear of the alternator (at 2 o'clock). It seems pretty strong as the arc makes a tick sound that I can hear over the flowmasters. The external regulator also has a faint smoke trail coming from it. I originally thought that the smoke was just moisture burning off because I recently blew a heater hose near it. Now I think something may be wrong. Any ideas?

 

I'm feeling pretty silly right now.
It's missing the ground wire isn't it. I wonder why my old inline 6 alternator didn't have one.

 

Did you get this fixed? The wiring looks right, when compared to the '72 diagram. Alt & reg are grounded through the cases. Wire colors and styles match mine, too.
Do you have a voltmeter to measure output when running?
The sparking is bad, so do not run longer than neccessary.
If this is a mechanical regulator (looks like it) and coolant got sprayed into it, I would suggest replacing it (and with a solid state one (looks & plugs in the same as the mech. one)).

 

A ground wire will always help. Lady72nRob71 is right about the alt grounding thru the cases. The sparking means either the bolts are not tight or the alt is not grounded due to paint. If you are going to rely on the alt ground wire make sure it is the same size as the hot wire or bigger.

 

Is the arcing inside the alternator? If so, you probably need new brushes.