So my buddy told me to turn the car on and disconnect one of the battery cables and if the car keeps running this means the alt is ok, but if it immediately shuts of after disconnecting this means the alt is shot. is this a proper function check for the alt, or will i have to pull it off and take it to autozone and bench test it?

 

I'm new to Mustangs, but I would NOT do this! Trying to run with a cable unhooked can damage some systems. Use a multitestor at the battery posts, or buy a digital plug in to the 12V receptacle voltage gauge. You can find these at many of the car parts stores. I like these because you can read voltage as you're starting, idling, driving, etc.

Normally, a fully charged good battery will read between 12.5 to 13 volts. When cranking to start, this will drop to 11.5 or so. When running with battery charging, 14.2 to 14.5 is okay.

Beware of OVERCHARGE. Sometimes a failing V. regulator will overcharge your system. This can fry wiring, pop fuses, all sorts of bad news.

(edit) With todays new cars and their parasitic battery drain, I stongly suggest the purchase of a "battery tender" type device. Especially if the car isn't driven frequently. These give you a trickle charge in, usually at less than 2 amps, will automatically shut themselves off when your voltage reaches 13. I use a "battery tender plus" brand, but there are several to choose from. Keeping your battery fully charged saves wear & tear on your alternator & voltage regulator. They'll last longer.

So, I'd say be sure your battery is charged, measure your voltage. Why pull a well functioning alternator since you can test the charging system while it's in the car?

One thing I don't like about my Bullitt...no numbers on the Voltage gauge, oil pressure gauge, etc. I'm an old guy car nut...I prefer numbers on gauges.

 

You can do that, but its not gonna tell you much other then if the alt can't make enough power to run the car. Just go to any parts store they can test it for you no problem.