02 F350 batterys keep losing charge

[fathead]

Here's the deal

02 F350 w/7.3L Needs jump started most mornings, especially over the weekend if I don't drive for a few days.

Disconnected both Neg on batteries, ran a test light between neg. post on battery and neg. battery cable, test light lights up.
Pulled every fuse, one at a time, every relay, one at a time, disconnected GPS, race radio, amber light, main fuse for stereo amp. Etc, test light stays on. Disconnected alternator, stays on...
The only time I got the light to shut off was when I disconnected a big wire, (8 gauge or so) that is on the driver side battery, goes thru a fuseable link mounted on the drivers side fender well, and into the fire wall. Don't know where it goes from there.
Parked the truck last night @ 10:45pm, the GPS showed 13.1 volts. Shut off the GPS, removed my cell phone charger from the cig. lighter and went to bed. This morning @ 7:45am the GPS showed 12.1 volts when I turned it on, truck started.
One other thing I have noticed, is that sometimes the alternator won't start charging until about 45 seconds after start up, so I
cleaned my battery terminals real good last night and spayed the purple stuff on to fight the green stuff.
Any ideas where to look next?

 

[Co-Dog]

The wire with the fusible link probably goes to the fuse box in the cab. Did you try pulling the fuses from there?

If you have an external voltage regulator, try unplugging it. I have seen them go bad and drain the battery. The delay in charging also leads me to believe that it could be the regulator.

If that doesn't work, I would suggest that you disconnect the batteries after you have driven it. Let it sit for a few hours or overnight. Then check the voltage on each battery. If they are not the same voltage, one of them may be draining the other in order to equalize the voltage. That usually happens if you have replaced one battery, but not the other.

 

[loufish]

You need to be using a amp meter, not just a test light. Also there is most likely a LCM(Lighting Control Module) that needs 20-45 minutes to "time out"...This is what shuts off the interior cab lights when you forget to...

Connect the amp meter in line with the posistive cable and the battery, and check it after about 45 minutes...you should be under 100 milliamps...if not, then start pulling fuses again...

 

[DBMETALWORX]

Do you have a switch on your gps? I use the the baja 540, and it says in the manual to use a switch cuz it still draws power whens its off. Also as co-dog said, if you changed 1 batt only, the other could be causing your problem.. We learned the hard way that you replace both batts @ the same time.. You will basically be playing leap frog with your batt replacement, 1 then the other.. Good luck ..

 

[loufish]

True, one bad battery will draw down the good one...

 

[ML Racer]

Yer batteries are good, keep them, throw the truck away

But on a serious note, get a DC amp meter and find out where yer power draw is!

 

[mebuildit]

I had that happen too when my truck was new. It was the connector on the alternator wasn't snapped in all the way. Pluged it in and good to go.

 

[Baja Fool]

Do you have a switch on your gps? I use the the baja 540, and it says in the manual to use a switch cuz it still draws power whens its off. Also as co-dog said, if you changed 1 batt only, the other could be causing your problem.. We learned the hard way that you replace both batts @ the same time.. You will basically be playing leap frog with your batt replacement, 1 then the other.. Good luck ..

Yes, if you are using a hard mounted Lowrance GPS antenna it is powered separate from the GPS and should, as the instructions specify, have a separate switch for power.
It will kill the battery(s).....I know from experience.