They are stamped from the factory. The numbers are on the unit but hard to see.
I don't know where to tell, but replacement alternators range from 100-140 amps for that model year.On the top & to the right of the alternator you will find some numbers look for 3 numbers followed by an A which stands for Amps such as 105 A. The numbers are usually hard to see, you can take a piece of white chalk & rub over them to get them to show up better.
Well, if the alternator is on any type of vehicle that has been made within the last 100 years, it will be the 100 amp alternator. There is no such thing as a 1900 amp alternator for a car. The highest I have seen is about 150 amps, and that is a heavy-duty truck alternator.
Look at the back of the alternator, particularly the black plastic cover on the back. The black plastic cover on a 105 amp alternator will have a small opening divided into three parts. The 130 amp alternator will have multiple openings.
It is stamped on it. Look at it real close.
In most cases if it is an alternator then it has an internal regulator
Do you have a amp??if you do it could be that the amp is sucking alot of energy from battery.And I'm guessing u have a stock alternator take your battery to autozone tell them if they can charge it is free and they will tell you is your Battery is bad.. If you don't hav all this maybe you hav a bad alternator and it wont charge ur battery maybe u need a new alternator...,just take your truck to autozone and tell them if they can check your battery and alternator from there you will know what's wrong hope this helps alot I had the same thing and it suck
How to Tell If Your Car Alternator Is Bad Check related link below…
WATTS = Volts x Amps For me to tell you what kind of amperage you're dealing with you'd have to tell me what voltage you're using. Or you could simply do the math yourself. Simply divide the watts by the volts and you'll get amps.
Usually the appropriate warning light on the dash will come on if the alternator is not producing current. If you don't trust the warning light, take a volt/ohm meter and (making sure it is set on the DC reading scale) connect it across the output terminals of the alternator to determine if any current is being produced.
A quick way to tell if there might be a problem with an alternator is to remove the positive side battery cable from the battery while the vehicle is idling. If the engine dies, odds are there is an alternator problem.
Any auto parts store where you will go to buy a new alternator can tell you what you need.
Any place that sells Fram filters will have an application chart that will tell you the correct size filter for your Tahoe.