Battery Light?

[xceslimitd]

04 350 6.0L w/ dual alternators

So, the battery light comes on with the turn of the key and then goes off like it's supposed to. The truck starts but seems to be taking more time than it used to. After about 15-30 seconds, the battery light comes on and then goes off about 20-30 seconds later. I replaced the batteries in Aug 08 with two yellow top Optimas. I'm pretty sure I can rule out the batteries and I think I can rule out the alternators bc the light goes out and doesn't come back on until I start it again. I'm guessing the starter is going and drawing too much from the batteries causing the light to come on until the alts catch the batteries up. Thoughts???

[firefightermech]

See what the amps are on ur alt cable with a large load, wipers high beams blowers on high, a/c on and see what happens. your alt probable is on its way out.

[powerhoghp]

I agree with firefightermech, but dont rule out the batts because they are optimas or less than 2yrs old. Have them tested. One other thing you could try is swapping the battery locations to see if it makes a difference. Also test resistance on the starter cable.

[xceslimitd]

I appreciate the help. So far, this is what we have. I tested voltage off both batteries after having driven for 20 or so miles. I got 12.8 off both. Using a load tester, I tested both batteries. Driver side performed as expected with little drop in voltage. Passenger side however, dropped to around 8 which is no bueno. I haven't tested the alts. I would guess that I have one bad battery but what I need to know is why. Thoughts and ideas are appreciated.

[xceslimitd]

So, I replaced the bad battery (passenger side) a few weekes ago and tested the voltage off both alts. At idle (approx. 600 rpm I think). Voltages off both alts with no load was 13.6. Voltages off both alts with a load (headlights, stereo, max A/C and high blower) was 13.3.

Due the reoccurance of the battery light coming back on after starting when truck has been sitting for a couple days (minimum) I started to consider the possibility that there was a constant draw on the system. After disconnecting both negative terminals I used a Fluke (10 amp setting) to measure the amps from the negative post to the negative cable. I had read that a measurement of more than .25 amps was a significant draw on the system. With a measurement of .28 amps I started to remove fuses and measure as I went. When I removed fuse #19 (Body Security Module/4x4 Module) the reading dropped to .11 amps. This obviously controls my power locks and remote entry. Now, even though that particular fuse accounted for .17 amps of the .28 amps, it seems that the remaining .11 amps is still a little high. That being said, I will continue to pull fuses and measure when I get home after work and post my results. Until then, I have a few questions.

Where is it (Body Security Module) located and does it control anything else?
What is the 4x4 module, what does it do, and where is it?
Any tips, tricks or suggestions?

Thanks for the help.

[mmccraney]

Originally Posted by xceslimitd

So, I replaced the bad battery (passenger side) a few weekes ago and tested the voltage off both alts. At idle (approx. 600 rpm I think). Voltages off both alts with no load was 13.6. Voltages off both alts with a load (headlights, stereo, max A/C and high blower) was 13.3.

Due the reoccurance of the battery light coming back on after starting when truck has been sitting for a couple days (minimum) I started to consider the possibility that there was a constant draw on the system. After disconnecting both negative terminals I used a Fluke (10 amp setting) to measure the amps from the negative post to the negative cable. I had read that a measurement of more than .25 amps was a significant draw on the system. With a measurement of .28 amps I started to remove fuses and measure as I went. When I removed fuse #19 (Body Security Module/4x4 Module) the reading dropped to .11 amps. This obviously controls my power locks and remote entry. Now, even though that particular fuse accounted for .17 amps of the .28 amps, it seems that the remaining .11 amps is still a little high. That being said, I will continue to pull fuses and measure when I get home after work and post my results. Until then, I have a few questions.

Where is it (Body Security Module) located and does it control anything else?
What is the 4x4 module, what does it do, and where is it?
Any tips, tricks or suggestions?

Thanks for the help.

Most of the time you need to let the truck sit after shutting it off for a while to make sure the computer crap shuts down. If you don't, you will get a false-high reading on your meter for parasitic draw. I think a half hour or so should be enough time...

[xceslimitd]

It had been sitting for about 2.5 - 3 hours after the drive in before I started testing and pulling fuses so I think I had that covered. Thanks for thought.

[xceslimitd]

Got home from work, disconnected negative leads on batteries, and turned on high beams for 30 min. Confirmed first tests of .17 amp draw off BSM/4x4Module. The remaining .1 amp draw is coming of fuse #35 (Instrument Cluster). I have cross country trip w/ 38' 5th wheel quickly approaching and need to figure this out. Thanks again for help.

[xceslimitd]

Still working the issue and have some new info and a question. Measured voltage off both alts at idle and at 1500 rpm. With no load, both alts measured around 13.88v at both idle and 1500 rpm. With load (stereo, brights, interior lights and max AC) alts measured about 13.2v at idle and 13.65v (lower) 13.8v (upper) at 1500 rpm. Autozone also tested while in truck at idle and got thumbs up for both. Both alts seem to be with in specs and both batteries still test good. Load tested them myself and Ford tested them. Any thoughts? What should resistance of starter cable measure? Thanks.

[rizzlebizzle]

Did you resolve this issue?