Any Alternator experts out there?

[jerryb1]

90 300 SE.
Can some one tell me what the field winding resistance should be on this Bosch regulator? I had an intermittant charging problem described on another post. I took a regulator from a 91 300SE and put it in with the battery disconnected(neg terminal) When I hooked up the terminal it sparked and blew out the regulator. Car off. Since the regulator only has three terminals, ground and the two brushes, I can't imagine why this happened. I thought maybe the field windings are shorted. The two regulators appeared to be the same. The 91 had a cap or resistor accross the top. Replacement parts call out for the same regulator for both MY's Unless maybe one of the alternators were changed by previous owners and the two brushes are reversed. This is mind boggling to me.
Thanks for any help!