This may not be the correct forum but a question anyway. Are there any common problems that would drain the batterys? When the truck sits for more than two days the truck will not start without a jump.
When testing with test light inline on the negative side, the fuse that controls the under hood light, dome light, map light and glove box light seem to cause a decrease when pulled. I completely disconnected the under hood light with no change. Are there any more refined testing methods on FTE?

 

You can try an digital ohm meter between the "disconnected" battery cable (plus side) and the ground side of the battery. should have no reading with the key off, if normal.. If you have a reading, example like 5 ohms, start pulling each fuse until the meter goes no reading .. Pull the plus side cable of the 2nd battery while you are testing..Also pull the hood bulb..
But, first before pulling batteries cables, I would check your voltage at a idle at the batteries.. should be around 14.4 volt if your alternator is working properly..
Another test i would do also is to check both batteries with a hydrometer to see if any battery cells are bad.. Napa sell one for around $20.. easy to use..

 

you mean a digital Amp Meter!

 

double post....

 

I suppose you could use a amp meter also.. but checking the resistance of the circuit will also show you if something is working that should Not be, with the key off..
Example: If you leave the hood buld in place, you will get a 2.4 ohm reading.. Pull it and the meter has no reading.. by using the method I described in Post #2..

 

I had this same problem. Weak or no cranking after 2-3 days. I left the cable off the alternator while it sat for 4 days while I was out of town. Started right up when I returned. The alternator had some bad diodes that were drawing current. I changed the alternator and all is well again.

 

Thanks to all that have replied so far. I was just out doing some more checking. I had the digital ampmeter hooked inline with the negatives disconnected and was getting a reading of .017milamps. I pulled the #15 fuse under the dash and the reading went to zero. 15 is the GEM, PCM, ABS module and brake shift interlock speed control. Now I am really stuck! Anyone no where to go from here? Please don't say dealer. Thank you all for the help so far.

 

I am by far no electrician but I believe the #15 fuse under the dash should be pulling some current, one of them is I cant remember right off hand which one. I would say alternator is your problem, mine did the same thing. It would charge fine but as soon as you turned it off it would drain the batteries. The guy at DB electrical told me they got a bad batch of regulators and that was causing my problem.

 

Did you replace yours with a DB? I had the 130 amp DB on mine and it was causing the current draw. Bad diodes, so
I thought. It could have been the regulator, because when I took the cable "on & off" the post on the alternator a few times the draw stopped. I also noticed the case was warm even after setting all day. When did you talk with them? I may need to get in touch with them about mine. I put the stock one back on and no more current draw.

 

Yes I replaced it with another DB unit. The guy at DB said they got a bad batch of regulators, several people were having the same problem. He rebuilt me one with a Ford regulator in it and it has worked fine so far. I would definitely give them a call. I got the bad one in January. I'm on my third DB alternator within a years time.

 

Thanks for the reply. I bought mine about 9 months ago and have had this problem for awhile. Just now took the time to look for it. At least I have something on there now that seems to work. I was looking for the increased amp output, but got something else instead.

 

1500/.017 = 88235 hrs. This how long it would take to pull both 750 amp batteries to zero with a discharge rate of .017 ma.

What this means based on this information is you do not have a short. I suspect one of the batteries has a bad cell and needs replacing. Replace both and based on the .017 ma draw I think you will be ok, given your alternator is working properly.

 

X 2.. it should be a bad battery.. But just the same, you may want to have the alternator checked just to make sure it wasnt the cause of your battery problem..

 

X3 on the batteries. Check em both. Also ensure that both are rated 750 CCAs each.

 

Check the connection on your positive and negative terminals. I had this same problem tightend them down and started right up. Took me a while to figure it out but turned out to be simple.