The alternator doesn't care if it's connected to the battery or the solenoid end of the cable. I prefer the solenoid end, as that gets the connection away from the corrosive battery.
The alternator need to have a #10 gauge wire. Just to be sure, check the voltage between the alternator case and the actual post on back of the alternator. Should have battery voltage there at all times.
Like others said, probably just not up to enough RPM to get it started.
It is possible to have gotten 2 defective alternators though, especially if the came from the same mfg. Bad parts, bad assembly are always a possibility. Just about any auto supply can test them for you.