phish

the stang has to be jumped every time as of late. when i finally got it started and let it run after pulling the cables off it died while idling after a few minutes. battery says it was bought 12/07

Gun Jam

A test of battery voltage would say more than when it was bought....but ill put my vote down for alternator.

-Gun

BlkVelvet

The way the "electrical power plant" works is that the battery is for starting. Then the alternator takes over for producing the electrics. Say an alternator is rated for 100 amps and there is a big stereo that draws 130 amps, the rest is them delivered by the battery.

Since you said you disconnected the cables and it died, it points to the alternator. Now also alternators produce peak power at a certain temperature. Here is a spec sheet I found looking around the net. (cold vs hot)



Also found this
Why an Alternator May Fail
Extreme use or from exposure to extreme environmental conditions
An alternator may not function properly due to malfunctioning electrical connections, or because it is not being driven properly by the engine accessories belt

One thing is to try is to start it and drive it around for about 15 min, to warm it up, then take the battery negative lead off. This may determine that the you just had a cold alt. Also check your belt to make sure that the alternator is getting spun up.

Last note, just because a battery shows 12+ volts, it doesnt mean that it has the current (amps) to keep it going.

The easiest way to figure out is to take the car to a place like autozone that offers free charging system testing.

KMatch

An alternator will easily lose output at idle if a load hits it such as brake lights or some other load spike. If it runs at all on the alternator, it has output. It may be weak, and not guaranteed good, but if it runs at all, there's output from it. Discoing the battery is only a quick test to locate a dead alt, not to sort a weak one. Load test the 2 yr old battery. If it's a cheap 2 yr old battery, save the trouble.

Stepman

You need to check battery voltage when it running to figure this out. It could also be a dead regulator. Get someone to verify this but, on a Ford, if you "feed the field", it should put out max amps that can be seen at the battery. If you only have a volt meter, it will show up as 15 or 16 volts. (don't do it for more than a couple seconds) In order to feed the field, first, make sure you have power to the I term of the reg. (this could cause a no charge too) then, with the car running, put a jumper from I to the F term as you watch batt volts. If this makes it "put out" then the reg is bad.