Replace alternator and ALT light is on

[sublimer]

I replaced the alternator a week ago and it worked great!!! Just as I expected!

But, as of today (and on-and-off) the past few days the ALT light is on! My truck only starts if I jump it first. Then, when I rev the engine, I can get the ALT light to fade in brightness, then if I rev it enough, it'll go out...this doesn't seem good.

My thoughts are:

1. I bought a bad alternator
2. The voltage regular is done for
3. The belts may be a little too tight

Any thoughts? Y'all have been great so far!

[kuz367]

Sounds like a bad regulator to me. I've always made a practice of replacing Alt/regulators together. When one goes bad it oftentimes will take the other with it. Most auto parts stores offer a free alternator check. Have them do that to determine the state of the alternator and then replace what's needed.

[QC]

You need to charge your battery, with a battery charger, not the alternator. Alternators are not intended to charge a dead battery, they are to keep your battery charged. If your battery is so dead it won't start your truck jumping it and letting it run for 30 min. will not fully recharge the battery, but it will shorten the life of the alternator. Installing a new alternator with a dead battery is the numer one cause of "defective" alternators.

[Calfdemon]

Check that the rear of your alternator is not touching and grounding out on the engine block behind it. If the rear of your alternator touches the engine block, it can ground out and cause the entire charging system not to work.

[sublimer]

I took the alternator to AutoZone and they tested it and it failed. So they switched it. I also replaced the voltage regulator since it still had the original one in there. When I took it off there was a nice side spider nest/cocoon looking thing on the back, haha. They tested the new alternator just in case and it checked out just fine.

I jumped it and let it charge for a little, seems to be doing better. When it's idling and all accessories off it pushes about 12.5v when I pull the choke it goes up to 14.5-15v. I can only assume then that while driving the voltage is in the 14.5-15v neighborhood.

I also rechecked and retightened any cable that needed it.

I did use Sea Foam yesterday and it I need to change the oil this weekend, I'll change the oil and add some fresh fuel and see if I can't get the idling voltage up a little bit.

Regardless, it's better than it was yesterday, haha!

[Thunderfoot]

I jumped it and let it charge for a little, seems to be doing better. When it's idling and all accessories off it pushes about 12.5v when I pull the choke it goes up to 14.5-15v. I can only assume then that while driving the voltage is in the 14.5-15v neighborhood. This is normal

I did use Sea Foam yesterday and it I need to change the oil this weekend, I'll change the oil and add some fresh fuel and see if I can't get the idling voltage up a little bit.

This voltage changing just off idle is normal with this older style/design of alternator... This is also why just letting your motor idle will not charge your battery back up, as the alternator is not putting out full charge,,, the motor has to be higher RPM, as you seen, to charge it.

[sublimer]

I jumped it and let it charge for a little, seems to be doing better. When it's idling and all accessories off it pushes about 12.5v when I pull the choke it goes up to 14.5-15v. I can only assume then that while driving the voltage is in the 14.5-15v neighborhood. This is normal

I did use Sea Foam yesterday and it I need to change the oil this weekend, I'll change the oil and add some fresh fuel and see if I can't get the idling voltage up a little bit.

This voltage changing just off idle is normal with this older style/design of alternator... This is also why just letting your motor idle will not charge your battery back up, as the alternator is not putting out full charge,,, the motor has to be higher RPM, as you seen, to charge it.

Awesome, glad to know it's normal! I'm gonna mark this issue as resolved and hope it stays that way!

The next project will involve the suspension!