Battery Light

[91 Jimmy]

My battery light is flickering after start up. I just replaced the alternator last year. I have been charging the battery and am able to start it with the aid of a jump pack. Is my battery bad? Just wanted to get some input before I pull it and take it to get tested.

I should add, the truck was in storage for the winter.

 

[Hogback Fabrication]

Just because the alternator was recently replaced does not mean that it's good. In this case however, it sounds like it probably is.

Ideally you want to measure the voltage in the system while the truck is running, setting the ground on any substantial piece of metal on the motor and the positive on the alternator output. It should measure ~14V, that means the alternator is working.

If your battery light is flickering that means the voltage in the battery is below a certain threshold. Not sure what that is on your truck but a vehicle battery is typically 12-12.5. Cranking the engine over draws more power than anything else, if your battery was a little weak it may have dropped voltage a bit. Running the vehicle for a while (30 minutes or so) may fix everything, your battery will need to be charged (either by a charger or by a working alternator) before it can be tested anyway.

 

[91 Jimmy]

I tried to let it run yesterday to charge but it ran for a while and then stalled out. I left it on the charger all night and it has been running for about 15 mins now with no problems. Although, I do hear a slight whining noise when the load fluctuates... Do you think the stall out was due to low battery voltage?

 

[Fordum]

You seriously need to get a voltmeter. They are cheap, and will answer a bunch of your questions.

After it runs for a few minutes, turn it off and carefully feel the big red wire coming out of the alternator.
It may be hot.
Feel it back a little ways from the alternator. If its real hot, odds are you have a shorted battery and that is what is sucking all the juice out of your new alt.

An engine will stall due to low battery voltage, and your light flickering indicates low voltage.

But, unless there is a huge load on the system, your alternator should be able to power the truck as long as its running.

If the battery was also stored all winter, and not kept charged, its probably bad. Especially if it was not stored in a heated place.
A discharged battery will freeze and be destroyed internally.

If you have V-belts, make sure that the alt. belt is not slipping. That would cause the whole problem too.

Fasted way to narrow it down, temporally swap with a known good battery and see if the light keeps flickering.
When you are taking the old battery out, look close at the terminals when you take them loose.
Might just be corrosion.