alternator shorting out?

1995 Kenworth T600, started having issues. Over night the battery's were dead. Charged them back up, and there all new. When I went to put the ground cable on. It arced when I touched the cable. So that tell me I have a short somewhere.
Today hooked the battery's back up. Took the power cable off the back of the alternator . No more arch at the battery cable. So I'm thinking the Alternator is shorted out? Would I be on the right track? Will wait and see in the am. If there's a draw on the battery's. If there still up, will go and get a new one to put on it. It has the smaller Alt on it. Ground wire and single wire. Does not have the quad mount alt.
Pete

 

Left the cable off the Alt all night, truck fired right up this am. So will get the Alt Rebuilt tomorrow am. We have a local guy, that does a great job. And sure saves some cash. It has the Deico Remy 22SI on it.
Also battery's are all new, Replaced the top 2 in Tx when we picked the truck up. And put the bottom 2 new on first of the week. I thought it was going to be the Alt. As it did not run the battery's down for over a month. Then started overnight.
Pete