test alternator output?

Is there anyway to test the output of a alternator, to see if it will still have enough power to charge a sound system?

well, first off, the alternator doesn't charge the sound system. it charges the battery which provides power to youe stereo. depending on what kind of power your running for your system would determine what you need to do, if it's just a small amplifier that only have 40 amp of fuseing, don't worry to much, but if your drawing 100+ amps to run your system then you need to consider some upgrades. if you have any doubt read up on upgradeing the "big 3" (stickyed at the top of this forum i beleive) and maybe upgrade to a ultima yellow top or some other deep cycle battery that would work in your aplication.

Well that's actually not true either.  When the alternator is working it would be charging the battery and providing current to your stereo.  The alternator will be operating at roughly 14 volts and that's what your amps will be operating at while the battery is only 12 volts.  This means your amps will be getting their power from the alternator and not the battery.  The only time the amps get their power from their amps is when the car is off or the voltage dips below 12 volts.

Can you simply hookup a DMM set to 'DC voltage' and rev the motor to see what amperage it peaks at (accesories off, of course)?

I actually always wondered this, just didn't think so since I haven't seen anything about it before.

Morning J   You can use a DMM on the voltage scale to see if the alternator is putting out Voltage.  To get the output current of the alternator it is a little more complicated.  That requires a clamp on DC current meter and a battery load tester.  Any reputable alternator shop will have the equipment needed.   Clamp the meter around the charge wire and connect the load tester to the battery.  When the load tester pulls the battery down the alternator will do its best to get the voltage back up to 13.8 thus producing all of the current it can.    

If you are using a DMM on the voltage scale, it is better to turn everything on, Lights, Air Conditioner, Stereo System Etc.   With all accessories on you will be demanding the most out of the alternator.  If it is able to increase the voltage when the motor is rev ved slightly, this ONLY means your alternator is working.  It will not tell you how much current it is putting out.

Sweet. I work at a Napa attached to the side of a Carmax (we supply their parts) so I have access to the stuff. I'm actually on 'vacation' until Tuesday after next (weee!) so it won't be until then. Thanks.

Big3, for sure. I think you're in the same boat as me. I've got 95a max system power (plus an extra Yellowtop) being powered by my stocker 105a alt and have been burdened by the dreaded 'whine' so I think i'm'a have to replace it. I do need to try one other thing first, though (outer sheild solder joint in my amp, thanks again- i am an idiot).