96 PSD Battery Discharge

[DixieDirt]

Hi all. If I let my truck sit overnight, by morning the batteries will be discharged enough for it not to start. The truck has brand new new 1000 amp batteries. What would cause such a big discharge in such a short amount of time? I know I need new battery cables, could that be the problem? I tried disconnecting the alt overnight but that didn't make any difference. I have determined that there is power going through fuse positions, 4,5,8,9,12,13, and 16 in the cab and positions 1,2,3,4,8,9,10,13,15,17,18,19,20 and 21 in the PDB. I don't think all those fuses should have power when the truck is off with the key in my pocket or should they?. So what do yall think? Where should I go from here?

[pipelayerjdh]

I would disconnect the starter and the starter relay and check for the draw. Also could be a bad ignition switch. How did you check the fuses?

[clmtng]

you know, good question that I'd like to know as well.

[CELAYORK]

I found this in my PC, maybe it helps:
Ok here is how you find a draw on the bat. Unhook both batt and the battery that goes directly to the solenoid which is the main battery. With the auxiliary battery totally unhooked unhook the main battery on the positive side only. Put one side of a test light on the positive side of the battery and the other on the cable end with it unhooked of course. If it lights up brite you have a good draw on the battery, if it lights up real dim you have a slight draw. Then if you have a draw rig the test light up where it will stay in that position without you holding it. Heres where you might need some help while you or someone watches the test light start pulling fuses one at the time. When you come to one and the light goes out that is the circuit where your draw is coming from. If no fuse turn the light off you need to unhook the alternator and see if it goes out. That is pretty much it. If you have any more questions just reply back. Oh yea if you open the door it will cause a draw because it is trying to turn the interior lights on. Try to rig the door switch where it thinks the door is closed. Hope this helps

your best bet is to use an ammeter in line, and wait about 5 minutes for any accessories to kick off, there is usually an "excessive" draw for a few minutes then for reading can be take, i believe fords spec on those trucks is around an amp of draw but if yours is as bad as you say it is then when you hook up it will have a whole lot more reading on there, but then go with mustang and pull fuses, starting with things that would cause the most draw, use your owners manual


Check your alternator when everything is cool.
________________________________________
Turn it off and leave it hooked up overnight maybe with a charger hooked to it and see if the alternator is warm in the morning or at least after a couple of hours after the engine is cooled down. If it's turned off and everything is cool except the alternator then the alternator is internally causing your drawdown on the batteries.

If it's sitting around keep the battery grounds unhooked until you want to use it and use a charger to keep the batteries charged, not the alternator. Don't just jump it to start it and then run it to let the alternator charge it up. The alternator is an expensive unit. Over-using it like that will kill it. It would be much better and cheaper to buy a battery charger if you don't have one and use that to keep the batteries up until you locate and eliminate your electric draw.

Have you checked the current drain with the truck not running? Maybe the battery is old and has internal leakage. (Not un common.)
:burnout

[pipelayerjdh]

Originally Posted by CELAYORK

I found this in my PC, maybe it helps:
Ok here is how you find a draw on the bat. Unhook both batt and the battery that goes directly to the solenoid which is the main battery. With the auxiliary battery totally unhooked unhook the main battery on the positive side only. Put one side of a test light on the positive side of the battery and the other on the cable end with it unhooked of course. If it lights up brite you have a good draw on the battery, if it lights up real dim you have a slight draw. Then if you have a draw rig the test light up where it will stay in that position without you holding it. Heres where you might need some help while you or someone watches the test light start pulling fuses one at the time. When you come to one and the light goes out that is the circuit where your draw is coming from. If no fuse turn the light off you need to unhook the alternator and see if it goes out. That is pretty much it. If you have any more questions just reply back. Oh yea if you open the door it will cause a draw because it is trying to turn the interior lights on. Try to rig the door switch where it thinks the door is closed. Hope this helps

your best bet is to use an ammeter in line, and wait about 5 minutes for any accessories to kick off, there is usually an "excessive" draw for a few minutes then for reading can be take, i believe fords spec on those trucks is around an amp of draw but if yours is as bad as you say it is then when you hook up it will have a whole lot more reading on there, but then go with mustang and pull fuses, starting with things that would cause the most draw, use your owners manual


Check your alternator when everything is cool.
________________________________________
Turn it off and leave it hooked up overnight maybe with a charger hooked to it and see if the alternator is warm in the morning or at least after a couple of hours after the engine is cooled down. If it's turned off and everything is cool except the alternator then the alternator is internally causing your drawdown on the batteries.

If it's sitting around keep the battery grounds unhooked until you want to use it and use a charger to keep the batteries charged, not the alternator. Don't just jump it to start it and then run it to let the alternator charge it up. The alternator is an expensive unit. Over-using it like that will kill it. It would be much better and cheaper to buy a battery charger if you don't have one and use that to keep the batteries up until you locate and eliminate your electric draw.

Have you checked the current drain with the truck not running? Maybe the battery is old and has internal leakage. (Not un common.)
:burnout

Good info, that's how I do it.

[DixieDirt]

Well, it seems that I have found the draw or at least what fuses are allowing the draw. Many thanks to celayork for the testing tips. Fuse position 3 (in the power distribution box) will almost stop the test light from glowing and fuse position 13 shuts it off completely. Without fuse 3 removed, the test light glows amost as brite as if it were connected directly to the positive and negitive side of a good 12 volt battery. Now what exactly do the fuses provide protection for?

[pipelayerjdh]

I think 13 is for the brake lights, let me double check.

[alberta 7.3]

fuse 3 in the under hood box is horn/DRL/flash to pass
Unplug your daytime running light module (if you have one) on the rad support below the driver's headlight (reach up under bumper) repeat test. I have seen these things go wonky and either have fluttering on-off headlights (ign on or off) or just kill the battery.

fuse 13 feeds the in-cab fuse box, so things like radio memory and such