Alternator Problems

Hi Guys !

I have a 68 Dart Gt with the factory 318, automatic transmission and factory a/c. It's been restored now for about 5 years. I have had to put two alternators on this car - they are NAPA reman alternators - and now it need another as it is not putting out the correct amps - it's under 12 amps - ....
Any help would be greatly appreciated !
How are you measuring amps?