I have been beating my head against a wall with this drain. In the process of my checks I noticed a sound under the hood, a very faint hum and I can not pinpoint the location. the sound is occuring when vehicle is in park with key removed.
As i was pulling fuses looking for the source of the drain I noticed that pulling the fuse in the No. 7 position makes the humming noise stop.

The fuse is designated to Dual Alternator "a" field
I do not have a dual alternator....

any Insights?
what else is in this circuit? Why is there even a fuse there since I don't have a dual alt?
could this be the source of my drain?

thanks in advance for your replies

 

There are several different charging systems listed in the workshop manual. I believe you have the version Ford calls "single generator with dual generator giveaway". I'm not sure exactly what that means, but here are the wiring diagrams:







It looks like fuse 7 is for the alternator field only. Were you able to measure the current drawn both with and without fuse 7 in place to see if it is the cause of your drain?

EDIT: (These diagrams are from a 99 manual; I didn't see the year of your truck so there might be slight differences)

Chris

 

First thing I'd check would be the GP and AIH relays. Those can get stuck and cause the batteries to drain down pretty quick. They would make some noise as well.

However, since you pulled fuse #7 than your alternator is the suspect. Fuse #7 is for the primary alternator, fuse #5 is for the secondary unit. Here is the diagram.

I think I'd disconnect the batteries until you get the issue fixed....

 

Have the alt tested. It may be getting ready to completely go on you..

 

Hmmmm...???

Now that I look at that diagram a bit closer...
It appears the power wire from fusible link B runs to the GP relay first and then over to the primary alternator.

What happens when you disconnect the GP relay? Does the noise stop?

 

Subscribed

 

Put the batteries on a charger over night with the fuse back in. If the alternator is bad and the field is energized, the alternator will be warm. That is about the easiest way I have heard to check it.

I thought I had a bad alt a last winter, but it was a bad battery, that was less then a year old that caused it, it would start fine if I drove it everyday, but if it sat more then a a day it would have to be jumped.

 

thanks for all the replies.
It looks like one of my batteries is fried, upsetting because they are both less than 1.5 years old. remanned alt was installed about 2 months ago.
one battery took a charge and passed a load test, the other will not take a charge and is sizzling inside so i quit trying to charge, the sizzling cant be good!
I guess my thinking now is that the hum i heard before may be a result of too low voltage. After a trip to Napa in the morning I will see for sure.

 

i also noticed that the alternators field is still energized ( the pulley is magnetized) although when I unhooked it completely I didnt see a noticeable drop in the battery drain. I guess i will assess this again tomorrow after the new battery is installed.

 

Don't just replace the one, you always do batteries as a set. If you bought them there, they should warranty them both out as a set. If you do only replace one, chances are you will be doing it again in less then a year, as the old one will kill the new one.

 

I followed yalls great advice and bought two new batteries, NAPA Legend 75. I was able to get one warrantied but not the other, but I replaced it anyway and kept the core to have a spare. Everything seems ok but I will give it a few days and see if the drain shows up again.
Thanks for the advice
Love this site and all the great minds here

 

If you kept the core for a spare...I would put a battery tender on that battery if you ever want any use out of it. If it sits too long without a charge it will be completely toast in just a few short months.
Dwayne

 

I found out the hard way that those battery tenders are just for maintenance, not for recharging batteries. I have one I use on my quad. It has a remote winch control on it and will pull down the battery over a matter of a few months. It will recharge an maintain a slightly discharged battery, but if it is low at all you MUST recharge it fully with a normal charger before putting the tender on it. I found that out when I called the battery place cause my $120 gel cell I put in the quad completely crapped out one week after the warranty expired. It is not fun pull starting a 700 cc quad by hand.

 

Funny thing about this. If you have a bad battery under Ford warranty, Ford will only replace one.

I used to be religious about replacing both.

I'm not anymore. I understand the theory- but my experience here is that the same side always goes to hell first. This suggests that the batteries age differently- I'm guessing one side is hotter or is loaded / charged differently even though hooked in parallel. So- my new theory is that a pair of batteries in this application is alike for a very short period of time before their performance differers from one another due to age. And since they spend most of their life with different capacity, I've stopped trying to match them both if only once fails.

 

I think your dealer is mis-informed.

The dealers in my area have always replaced them in pairs, even if only one tested bad. I've had batteries go bad in Tucson, Phoenix and Albuquerque...each time the dealer replaced them in pairs.