PennSilverTaco's "Perfect 5-Lug Regular Cab" Build, Aspergers, and General BS MegaThread!

It could be the alternator, or it could be something pulling the battery down while the truck is off.

Both can be checked. But one is a bit more involved. It’s called a parasitic draw test.

Check and see if anything is being left on when the truck is off.

 

Very little to be left on; I am sitting in the truck right now and I checked the dome light, which is off. I will probably start unplugging the dashcam and phone charger when I park the truck for the night.

On another note, I left my dome light on by mistake for several hours in bitterly cold weather while I was at work almost four years ago. The truck barely started, but it did start and the alternator was able to recharge the battery. That battery was an Interstate MegaTron installed in 2014, the dome light was left on in late 2018 or early 2019, and I finally ended up having to replace that battery in September 2020. Driving with a cooked alternator in December 2021 destroyed that battery, which came from AAA, and I replaced it with the Optima in early 2022 if I remember correctly. I going to be really pissed if my Optima gets damaged by an electrical issue, because this is the most expensive battery I've ever bought and it's supposed to last for several years longer than the typical battery!

 

Was the replacement alternator new, OEM, reman OEM, or ???

I don't buy the 'false positive' theory. Not to say it couldn't happen, but I'm skeptical.

Based on everything you've said, my testing would be the following:

-Alternator charging? (DVOM on battery w/ engine running. Should be >13.5v)

-Battery load test

-Parasitic draw

From there, there's a bunch of other things, but that's the big-picture stuff to start. You can also pull the alternator most large parts stores will be able to bench test it.

 

Where did you get the alternator from? If you get from an auto parts store they will be hit or miss.

 

I believe the battery light doesn’t actually come on with a weak battery. The battery light is basically a charge warning light. The light comes on when the alternator is failing to charge at an appropriate rate.

It’s been a while since I actually studied the workings of the light. But best I remember, the battery light doesn’t come on just because of low voltage at the battery.

There’s actually a terminal on the on the alternator it’s self that controls that light.

@Dm93 or @Bishop84 can confirm this.
As I’d actually like to know “for sure” if this is how it works. And if so, I think the battery light should be changed to a charge warning light.

 

Correct the alternator controls the battery light by grounding the L terminal, the only other things that could cause the light to turn on are if that wire is shorted to ground or the instrument cluster is malfunctioning.

 

There was a quick flash of lightning last week outside the garage, went to flip on my air compressor and the capacitors were fried.

 

X2.

 

The alternator did in fact come from AutoZone, and a voltage test confirms that it is not charging the battery properly. My mechanic ordered a Denso alternator from his supplier for $250 and is going to install it on Thursday. As of right now, the alternator is operating at roughly 70% capacity, where as the one it replaced totally died.

 

I just had the same thing happen. It was the after market alternator connection. It was tight but had a little corrosion going on. Quick fix with a wire brush.

 

Much better choice on the Alternator this time. You’ll be up and running in no time buddy

 

I'm up and running right now, but seeing if my alternator will last until this Thursday is like playing Russian roulette...

 

the lamp positive is connected to a fused +12V source and the negative is connected to the cathodes of the diode trio in the alternator which provides the feedback to the VR. With a failing alternator the output of the diode trio falls further towards 0V and provides enough potential to light up the battery lamp which is actually a charge indication lamp in reality.

 

That’s definitely an in depth answers. Thanks.
Now, I just have to know what a diode trio is to exactly how it works.

But never the less, you and DM93 answered my question.
The light doesn’t come on due to battery state, it’s charge state.
Thanks guys!

 

It's basically a rectifier bridge that supplies DC power to the voltage regulator for the field coils.

 

Autozone has lifetime warranty, which means you'll be replacing the pos alternator we sold you with another pos alternator every few months for the rest of your life. Optima batteries used to be very good. My last one made it 3 years before if failed load testing. If you have a battery charger you can hook up to charge overnight, that'll get you by until the alternator gets replaced later. If you have a jumper pack, or know someone to borrow one from, thats extra insurance to keep you from getting stranded.

 

In other words...

This


Equals

This


#science&stuff

 

technically those are the output diodes, the diode trio is only a half wave bridge rectifier. But yes, science indeed

 

Ahh, Now is see the problem. The squiggly lines and triangles are broke.
Makes perfect sense