Kent,

Since what you have is a repowered SM, I am not sure that I can help further without knowing more. I think it is likely that the issue is a loose connection, but could be an internal problem with the alternator, like a blown diode. I am not sure which 24v alternator you have, and that may be the reason for no excitement at high rpm. 

Maybe try to locate the small relay shown on the right side of the photo I included...if/when you find it, trace the wires to find the one that goes to the excite connection on your 24v alternator, assuming it has one and does not rely on internal excite.