My truck was slow to turn over this morning and I thought it was strange, but forgot about it at work. At lunchtime, I went out to the truck and barely turned over and just wouldn't start. My batteries are a month old and the alternator is a 6 yr old motorcraft. I took off the alternator and had autozone test it. It failed every test. While I didn't want to get one from AZ, I had no choice, it was only thing around. I put it in, got the truck jumped and drove it home about 25 miles on the highway. My voltage meter didn't seem to get quite as high as it was with the old alternator. I checked the batteries and they are at 12.4 V and the alternator is putting out 12.4V at idle.
The question is: Shouldn't the batteries be showing at least 13V by now? And shouldn't the alternator be putting out more than 12.4V at idle?

 

Check the connector to the alternator for damage. Battery light come on when the key is in the on position?

 

No damage and battery light comes on.

 

I was told this by a very knowledgeable Interstate battery tech that had a interstate battery and electric shop for several years. My car had quit charging so I stopped there to have it checked out that part was free. He sold me a new alternator and installed it for a very reasonable price. Now this is the part that is interesting he told me to put it on the charger when i got home and let it charge overnight. What he said was the alternator would never fully charge the battery unless it was fully charged to start with. It's been the only time i have ever heard that, but i have always done that whenever i have a battery run down for what ever reason.

 

It was already too late. You should charge the battery as much as possible before driving anywhere. After the regulator gets a chance to break in (various thermal cycles) it can take a lot more abuse than brand new. To get your alternator to live a long and healthy life, charge low and slow, not just a quick high amp top charge before driving the vehicle.

 

...and this means what to me at this point?

Am I just SOL?

 

Just put it on a long slow charge at least overnight and you should be good to go. I think batteries always have a little shorter life when they get run down, but you will most likely get several years out of them.

 

If you can't get 14v out of the alt... something's wrong. Maybe it was no good from the store. Check fuses, charge up bat. with charger. Maybe take the alt back for a warranty or at least a spin check.

 

I had a batt with a intermitant dead short in it and it would look good. Then the cables can have internal corrosion that when coupled with heat can cause more load resistance.

GPR welded plates can cause a draw too. I had the third brake light drawing a lot of volts to the point that the connector melted.

You can always remove the power lead to the GPR and see if its any better. Bad neck sleeves on GPs allow direct grounds too; the gp can swell and crack them.
The FB Heater plate coil can cause a draw that wont burn out f-22
Then the connector at the top of the alternator can also have issues with the wiring. Its a favorite hand rest when we work on them so its another place to check. As well as belt slippage which is a low potential since you normally notice that with the brakes. Then trailer wiring harness are a sneaky one that can cause some slow draw too. Test the voltage relay to amke sure that the ckt is open when the truck is off-- passenger side fender just south of the batt. Same spot that a lot of people tie in alterante ckts. Routing alternate ckts from the voltage realy is not too bad if the proper fuses are use.

Any how just thought I would give you a few more checks and best wishes on it.

 

Thanks for the replies.
My glow plugs are only a year old. I don't think that will be the issue.
I checked the power coming out of the alternator and it was reading 12.4V If I had a short further on down the line, I should still get a slightly higher number at the alternator, shouldn't I?

I will try to check all of these things out.

BTW, 3 year replacements on the batteries from AZ. This is my second pair. The last ones died 2 weeks before the warranty was up. good timing.

 

Are you measuring after you have determined that the glow plug relay has cycled off?

 

You should be seeing charging in the 13.6 - 13.8 range, maybe up to 14 v.
Charge up the batts with a charger overnight and re-check output in the am. If it's still 12.4 v take the alt back and get another one, or go buy Motorcraft and return the defective AZ alt.