Alt vs Voltage regulator

Hi guys. I know this information is in this forum somewhere but for some reason I cant access it. I find this forum extreamly hard to navigate. Might be my platform, Might just be me. I apoligize. My question is... If I have 12 volts at the battery after chargeing. and no increase in voltage when the car is running, and the ALT light is on, how do I know if its the voltage regulator, or the alternator thats bad. Again I apoligize for not being able to search this toptc.

Video of testing  Ford G1: 

Thanks Rocketman. I watched that vid. several times, I didnt like the part where the voltage shot up to 18v. Decided to pull the alt. and have it tested. The alt rebuilder said my alt was fine and it was a good call not to spike an already fragile electrical system. He ordered me a heavy duty voltage regulator. I cleaned all my connections and grounds and hope to get the regulator in today. Again thanks Rocketman

That's called a stress test, checks out the other weak points at the same time you're testing the regulator. That's why the Ford tester has the knobs on it, reduced voltage to the field windings and gradually increase the voltage to see if the alternator reacts.