Driving home yesterday when I noticed that the mattery light came on and the amperage was slightly low. When I got home I checked the battery and the little viewing window was red instead of green...I'm thinking low battery thought truck cranks fine...for now. Went to a friends house about 3 miles from mine, stayed till dark. The battery drained almost completely; I couldn't hardly see with the headlights and the window would not even go up. Did my alternator quit charging or just a bad battery?

 

That window just shows what's happening in ONE of the battery's 6 cells. So it's possible that the rest of the battery is OK.

But if your window wouldn't roll up with the engine running, then it sounds like the battery is weak because the alt. isn't charging, so the entire truck is running off the battery.

If you can see the back of your alternator & you have a cheapo multimeter, set the meter to DCVolts, put it across the battery posts, let the engine idle, & use any jumper wire (a paperclip) to test the alternator. On the back, near the 3-wire connector, there's a hole with an arrow that says "GROUND HERE TO TEST". With the engine running & the screw in that hole grounded, the alternator will put out as much as it can at that RPM. Your volt meter should jump to at least 15; even higher if you rev the engine, but don't do it for more than a couple of seconds.

If the voltage comes up, the fault is in the voltage regulator or its external circuits. If the voltage stays low, replace the alt.

 

Thanks Steve....I took a chance and changed the Alt....It's fixed. Now I will just have to charge the battery or let the alt charge it.

It cranks...It runs....I'm like Taco Bell.....Good to go

 

The fact that your battery light came on and the amperage was low should have been a dead giveway that the alternator was bad.
The little light in the battery is pretty much meaningless. When my batter went bad this past summer, the light in the batter still showed green even though the batter wouldnt hold a charge.
A couple of years back the alternator in my truck went bad and it did the same thing. It would kind of stumble a little bit and when it did you could watch the battery light flicker and the needle for the alternator output would move back and forth a little.
Swapped out the alternator and it was good as new. I didnt figure I could complain, I got 140,000 miles out of the original alternator.

 

Well after I thought about it and posted the thread, it sorta slapped me in the face that a bad alt made all the since in the world.

None the less, it's done and I'll never have to buy another one!

 

That will void the warranty on the new alt because it will overload it.

 

Won't void it if you don't tell them you did it

 

Any decent parts guy can tell. If it's 3 days old, and doesn't charge, and stinks like #@*$^ or has smoke trails coming out, he knows what you did.

 

Lol the hard part is finding a decent parts guy. I bought an alternator for my truck. It was bad. Went back and they said it was fine. Put it back on the truck, it still didn't work. Took it back, they gave me a new one. Put it on, and it had a bad bearing that screamed whenever the engine was running. Went back again and they gave me another one. Most of the time they don't even ask, they'll just give you your money back. I guess it also really depends on where you bought it. This was at NAPA, and we all know how smart those guys are.

 

It's hard to find a "decent parts guy" at Advance or Auto Zone in these parts...or NAPA for that matter. If it's not stated in a book somewhere, they haven't a clue. That's why I use this forum

Like said above...most likely they will just give you another, no questions asked.