Hi,

My battery light is on all the time, voltage shows 8-9 volts and I''m not getting any increase in voltage from the alternator.

I have cleaned the cables/terminals and battery. All excellent. Also checked fuses which are all good. Battery had drained to around 8 volts, so I charged for two hrs at 15 amps. Brought the battery up to 12 volts, and all cells were the same specific gravity, but only around 1,100 sg. Did a load test and it showed great and strong (1000 cranking amps). put back in truck and started but still no charge.

My question is: If the battery is marginal, all cells the same and able to take a charge from an AC charger, shouldn't the alternator put 14.5 volts in the battery? Or could the battery showing only 1100 sg be too far gone to take a charge from the alternator. On the AC charger all cells bubbled when amps were raised.
I read about an inline fuse between the alternator and the selenoid but can't find it. and then there is a maxi fuse??
Just wanted to hear your thoughts on this before I buy an alternator if I really don't need one. Truck starts and runs fine. 99 6.8 f250SD

Thanks,
WM

 

It sounds like your alternator has bit the dust. Time for a new one !!!



RON

 

Ok, I put on a new alternator and the battery light is still on. I get 14.5v when running and 12.8v with key turned off.
Shouldn't the light go out as soon as it gets to 12+ volts? The maxi fuse must be good since everything works, but does anyone know about the 20A inline fuse?

Thanks,
WM

 

I had a similar problem. Alt was reading 11 volts at idle but battery light was not coming on. Replaced the alternator with a new one (AutoZone Duralast Gold). I checked it once after replacing it and it read 14 volts.

Soon thereafter, the battery light came on - only at higher rpm, not at idle. Didn't have a chance to check the voltage again, but the batteries drained out on me after a 1 hour drive. Replaced the alternator with the same one (lifetime warranty) and now it's charging fine and no battery light.

Maybe your new alt is bad, too?

Scott

 

I don't know anything about a 20 amp inline fuse, but I do know if you put a 99-02 alternator on a 2003 and up truck, it will charge properly, but the light will be on. I would think that the opposite is also true---If you put a 2003 and up alternator on a 2002 and down truck, the same thing would happen. The only difference between the alternators is the internal voltage regulator. Is it possible they gave you an 03 and up alternator ??? Physically, they all look the same.


RON

 

Thanks to all for your help. The new one is charging correctly. I went back to Advance Auto and did another test. It showed what I posted here above. 14.5 w/engine running and 12.5 w/engine off. The battery light still is on all the time though. It is possible that the years are wrong, my original had the Bat connection flush against the back. The new one has a tower and the Bat connection is on the top of that tower. Is there any way to switch a wire that would turn off the battery light? Armed with your explanation of the difference between 99 and 03 I'll go back to Advance and have them check it. I'll ask them to show me a 2003 and another 99.
I can't imagine having to work out these problems myself. This forum is a godsend.

 

Did they charge your battery? If your alternator bit the dust the battery was losing power as well since that's all you had as power up/sustained. They'll charge and check the battery for free. Not sure if that would throw that light or not. Eh disregard, apparently I didn't read that part of the post first time through.

 

Per my knowledge 14.5 volts is high charging voltage. Usually it is closer to 14 V. Maybe that is why you have the light on?
I replaced my alternator a month ago with one sold at NAPA. The light went off right away.

 

Yeah, I forgot to add, I replaced my alternator probably 2 weeks ago, light went off as soon as I fired it up.

 

I would recheck all fuses, including the ones for the dash. Sometimes there is an 10amp fuse that goes to the instrument cluster that blows when alternator bites the dust.

 

Edit My mistake

hope you get it figured

 

Hi,
I had high hopes for this as I hadn't checed the dash fuses before, but all fuses were fine. I'll check the 2003 alternators to see if that's what they gave me instead of a 99.

Am I safe to assume that the wires/connections on the alternator have good contact and installed correctly since it is charging as it should?

Thanks,

wm

 

Ron,
I found that on the wiring schematic for charging system in the Haynes Manual.

WM

 

See if any of these part numbers match what you have. Here are the part numbers from Auto Zone's website

99 6.8L

DL3501-18-10
95 Amp

DL3512-18-10
130 Amp

2003 6.8L

DL3620-16-10
110 Amp

 

Nope. Bought it at Advance Auto. Checked their numbers and it appears that they gave me the right one according to their catalog. They had a totally different list for 2003.

I charged the battery 6 hours or more today and the specific gravity didn't go up so tomorrow I will put in a new battery. Maybe that has been my problem to begin with and caused the alternator to burn up! I'll let you know as soon as I get the battery in there.

Thanks again for your support. I really appreciate it.
wm