Alternator not charging why?

I don't care about the check engine lite. Your saying you checked for codes and there wasn't any?

Take second reading across battery posts, engine running, The second reading should be higher than the first, is it? If it is higher, than the alternator is charging.

Hello,

This light comes on when the alternator has gone out here is a guide to help check it with a video on how to change it out.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

and

https://www.2carpros.com/articles/how-to-replace-an-alternator

and

https://youtu.be/d3dt5cQGhmM

Please let us know if you need anything else to get the problem fixed.

The two wires in question may or may not be hot, depending on your system. To check your alternator output, do the following.
With the truck at a warm idle, all accessories "off", meter on the 20 or 50 volt DC scale, test accross both posts of the battery. You should get a reading of 12.5 to 14.5 volts. Anything below this, your alternator is bad.
Then, one at a time, with meter still connected, turn your accessories on ie; blower fan, headlights, AC. The meter should not drop below 12.5 volts. Hope this helps.

Clean the connections on both batteries. Then have both load tested to be sure they are okay. GM ties them directly together so if one side has a bad connection and is not charging it will pull the other battery down. Check the connections on the alternator as well. Be advised that if you have one bad battery you will end up replacing both so they have the same ratings and the system works properly.

It could still be the alternator but start with the easy/free stuff first.

The problem could be coming from the computer's field generation control

Start with the very first reply unless the battery is less than two years old. It depends too on what you mean by "burning up". AC generators by their very nature are incapable of putting out more current than they're designed for. By installing a 145 amp generator you will not get any more current if the car doesn't need it, but if there is a defect that causes it to "full-field" or run wide open, you are likely to destroy the wire going from the output terminal to the battery. That wire size was chosen based on the generator the car was built with. Now it is capable of much higher current so you can expect more damage.

It is real common on 1987 and newer GM cars to go through four to six generators in the life of the vehicle and the way to reduce those repeat failures is to replace the battery at the same time. These generators develop huge voltage spikes that destroy the internal diodes and voltage regulator and can interfere with computer sensor signals. The battery is the main component that dampens and absorbs those spikes. As it ages, it loses its ability to do that, and you have numerous repeat failures. This assumes your term "burning up" simply means failing. If you mean wires are melting, the cause could be the same, meaning the voltage spikes are causing the voltage regulator to short and full-field the generator, or make it run wide open. That could result in wires melting, but if you have connections that are getting real hot, that is due to resistance. You solve that taking the electrical terminals off and shining all of them up to remove any corrosion.

The larger generator will not cause higher output on its own. It only has a higher capacity, just like a hydraulic pump on a piece of construction equipment will only pump the volume of fluid needed, even though it has a higher capacity than the old one. To melt the plastic insulator at the output terminal you have to have current that is constantly very high, (which those parts are designed to handle), or there is excessive resistance which in this case can be way too small to measure accurately with an ohm meter. We can measure the RESULTS of that resistance in the form of "voltage drops", but one point we would need to put a meter probe is inside the generator and is not accessible. Voltage drop tests are commonly performed in starter circuits. Since your connections are new, we can assume excessive resistance in the connection is not the problem. That would leave a defect in the generator when it was rebuilt or something in the vehicle is drawing high current.

If the problem is with something the rebuilder did or overlooked, it is usually due a new inexperienced person doing the work and there will be a whole pile of them with the same problem until it comes to the company's attention. The failures will all occur the same way and in about the same time. You'll solve that by going to a different parts store.

If excessive current is the problem you can verify that with a load tester with an inductive amp probe but you would still have to know what "normal" is. If you have an obnoxious amplifier many kids use or if you've added a lot of lights or other accessories, those may draw high current.

If the voltage regulator is sensing low system voltage it will run the generator harder and that excessive current will go through the battery and overcharge it. Normally that is not a problem on GM systems because system voltage is monitored right inside the unit. The notable exception is on vehicles with digital instrument clusters. They are affected by minute changes in supply voltage so they tap off that point and run a circuit to one of the terminals in the generator's plug and monitor voltage there instead. A problem on the cluster or in that wire can cause overcharging. You'd find that by measuring battery voltage with the engine running and comparing that to the voltage on that terminal at the cluster. They should be the same.

VERY happy to hear it's solved. Things like that are hard to diagnose over a computer.

Hi natesdogg113. Welcome to the forum. Start by measuring the voltage on the fat red or black wire on the back of the generator, and the small red wire in the plug when the ignition switch is turned to run.

Here is a wiring diagrams so you can see how the system works. Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.