Ammeter hookup HELP!

[Mark]

 Almost ready for fire in the hole.   Got some cheap gauges to keep tabs on my new engine.  The oil pressure and water temp was easy but the instructions for the ammeter contradict themselves.  Anybody have experience with these?  Guy at the parts store told me to hook to the positive on my alternator and the other to my power source, what do you think?   Oh and he also said don't mess up or you'll burn everything up, nice guy huh (not my regular parts store).  Any input on this would be appreciated.  Thanks  Mark