Put in new alternator,shows charging and battery holding charge but battery light stays on. You start car and light stays off for about 15 to 30 sec. than on.

What's the voltage at the battery with the car running ? Testing an not guessing is the way to do proper diagnostic's ! Battery light staying on , is there B+ voltage at the alternator connection's ? A new alternator won't make a bit of difference if no power to the alternator . Looking at a wiring diagram an testing the electrical circuit ,doing voltage drop testing , plus checking for DTC'S - diagnostic trouble code's . Some vehicle's charging systems are computer controlled . And looking at a wiring diagram i see your vehicles charging system is computer controlled . If you have done so already , take it to the dealer

Test the alternator. The battery light is for the charging system. Once the charging system is working with the engine running, the light should go off. If your light stays on with engine running, the alternator may need service or replacement.

To test the charging system, just put a voltmeter on the battery with engine running. The voltmeter should register at least 13.5 volts- alternator is charging. If you only show battery voltage with engine running, like 12.2-12.8 volts, the alternator or charging system is not working. The battery light should be on to signify this.

Maybe it wasn't running long enough to charge up the battery?
Stop trying to jump it, when you are having problems with it dying, take the battery off and have it charged. And/or buy a $20 voltmeter to see what the battery shows. If it says less than 12 volts, it is discharged, and needs charging. A good battery that is not run down should have at least 12.5 volts. A new battery that is charged should have very close to 13 volts, maybe 12.8 volts.
When you have the truck running, check the alternator for charging. You put the voltmeter right on the battery and check it again. This time, with truck running, battery should show at least 13.5 volts. That shows the alternator is working. A good alternator will put out about 13 or 14 volts-the regulator will keep it from going any higher to prevent problems, like a melting battery or electrical parts burning out.
I would say get the charging system working right, then address the problem of dying at stop lights. That could be a carburetor problem, if the alternator is working.

If battery light is on while engine is running, then the charging system is bad. That is, you will need a new alternator. If the battery is a couple years old, you may have now stressed it a lot also. Expect it to show signs of failure too, quite soon if not already. First thing is to change out the alternator. Put the battery on charge for a while too. Then after new alternator, see if you have weak starting problems over next week or so.

You have an electrical drain on the system. Look for lights that stay on with everything closed

hi, might wanna check the atternator ,check the belt make sure it still on .over time they get old and loose. if still on you could do a test, while the car is on diconnect the ground wire off, if the car stays on the atternator is good. if the cars turns off , you got a bad att. thanks hope been some help

How do you know alternator is good?
Put in a cheap volt gauge.
Should read 12.5 normal.
Down to 10 starting.
Back to 12.5 at idle.
Up to 13.5 when engine revved up.

But battery low on water will not hold charge.
Could also have internal short.
Volt gauge will show.

Could also have something staying on, like engine or trunk compartment light?
Pull one battery terminal, and see if test light lights up across gap. If it does, even weak, you have a constant drain. Could be alternator. When diodes go bad, alternator can drain battery. Disconnect things until light goes out.

is it charging sufficiently? short jorneys do not allways put enough charge back into a battery, is your charge light coming on then going out once the engine is started?

This is likely caused by a burned out alternator, charge the battery, verify it will hold a charge and replace the alternator.

Yes, by connecting the charger the wrong way round you have damaged the rectifier in the alternator, now needs a replacement