Hey guys. I am trying to diagnose a problem with my electrical system and I just wanted to confirm my findings with the gurus. Anyway, yesterday the battery light came on while I was driving home from the store. I parked the truck, turned it on and off a few times and the light always came back on. I opened the hood, looked around for loose connections and such at the battery/ground/alternator and tightened everything up. To my luck, I turned the truck on and the light went out. So I went to bed thinking I solved the problem. Today I went out in the cold (was 29 in NJ this morning) and turned on the truck to warm up while I went back into the house for some coffee. When I came back out 10 mins later the truck was off (the radio/ interior lights were on however). I tried to start it but it didn't have enough juice to turn over completely. So, I put a trickle charger on it and went to work. When I came home, I removed the trickle charger, took the battery cable connections off completely, a sanded/cleaned them. Got back in and she fired up with a lot of power but the battery light was on. I tested the connections while running with a meter and got 12.1 between the two battery terminal connections and also between the alternator terminal and negative battery terminal (did it this way so that I would make sure the wire running between is not the culprit). I had gotten over 13 across the battery terminals themselves after I took the charger off. So, I think I need a new alternator and was going to run out and get it. I know I should take the truck to the store and have it tested, but I don't want to run the risk of it shutting off and not starting again. Did I do enough tests or is there anything else I should check. Any help would be appreciated

 

If you peel back the sheath on the + batt cable, you may find the cause. If there's no corrosion there, I'd guess a bad ground somewhere. Pretty sure you should be seeing 12.4-12.6 from a good battery though. If you take it to the parts store and it dies, they will give you a jump.

I had corrosion...about 6" worth. Shop said they'd need a new cable which was about $400. If you clip a couple of the zip ties lower down, you can free up about a foot of + cable though.

 

I had thought that a corroded wire could be an issue and will go check it out more thoroughly. In the mean time I just came in from doing some tests. I did a voltage drop test from the negative battery terminal to the alternator casing and there was a .01 drop even with revving the engine. Same outcome doing a voltage drop from the positive battery terminal to the positive alternator wire terminal.
Here is where things get a little tricky. I turned the truck on before and the battery light was not illuminated like it had been before, so I quickly volt tested between the two battery terminals and got 14.1v. Tested it a few times and everything stayed the same throughout. So I thought maybe cleaning the terminals did the trick. However, when I went to turn the truck off I noticed the battery light had come back on. I then went around and got 11.9v between the battery terminals. I'm guessing that this cannot be a cable problem if it has this sort of sequence.
I did check that the serpentine belt was spinning the alternator in both cases and it was.
Is this a dying alternator? One second it works and the next it doesn't?

 

Alt or battery. You need to remove the battery from the vehicle to have it tested and if it checks out, then do the same to the alternator. Not every parts store can test an alternator (must be OFF the vehicle) though.

 

I just wanted to post the solution. I was going replace the alternator because I saw that the battery had held around 12.6v after a trickle charge (it had sat around 8 hours in the cold so I figured it wasnt at fault). Anyway after trying to get the alt out for about an hour, I finally managed to get it up and over the upper t hose of the radiator. After I did so I noticed that the little wire (Im imagining ground) had be severed down where it meets the larger plastic sheathing. I cut and spliced the wire back together and wallah, charging battery. Hope this helps someone in the future

 

No, that wire isn't the ground, that's the wire that excites the alternator so it starts charging.
Glad it was a cheap fix.

 

any way you could take a picture of said wire OP?

 

Its your alternator, its slowly dying.

Mine took me 2 weeks for it to die completely. The battery icon/light comes on randomly, i notice my lights started to dim when the battery light came on at time.

I was able to drive the car during the daytime for 5-8 miles. But not at night since I needed headlights and it kills your battery using headlights.
So during the daytime, if you have a charged 12.5-12.8V battery reading, you can make it for a short distance. Turn off all electrical (radio, heat, lights) to save battery.
You can run on a battery alone, but you will need a battery charger and charge back to full 12.8V again.

If your alternator is working properly, the reading should be 13.8-14.5V while your car is running so the alternator is recharging your battery. While your car is running, if battery the reading is less then 13.8-14.5V then your alternator is slowly dying or if it start to drop rapidly.

Get a new alternator!!!!! took me 4 hours in -10F cold to change mine, shouldn't be too bad for you since its getting warmer out.

Hope that helps

 

"No, that wire isn't the ground, that's the wire that excites the alternator so it starts charging."

i believe the man is correct, had the same problem with the same wire.

 

+2 with antichrist & drowssap.