Electrical problem
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Joined: Nov 2004
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From: Pensacola, Florida
Electrical problem
2005 6.0 King Ranch 82K
Just replaced both batteries which were definitely bad. Now, the new batteries are slowly going down when the engine is off. What could be causing the draw on the batteries and what is the best way to find the problem?
JimB
Just replaced both batteries which were definitely bad. Now, the new batteries are slowly going down when the engine is off. What could be causing the draw on the batteries and what is the best way to find the problem?
JimB
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Joined: Aug 2006
Posts: 17,398
Likes: 317
From: Whittier, CA
I would probably find an electrical shop as well, but since the question was asked here I will assume you would like to snoop this out yourself.
A couple ways to isolate the problem are -
Remove fuses one by one. Each time you pull one, listen for any clicks that might indicate a relay or device that was powered when it should not have been. Pull relays doing the same thing. A helper with sharp ears (SWMBO) under the dash or under the hood while you pull them is helpful. Be sure to listen for clicks as you replace each one as well.
You can also rig up a test light with a spare 12V bulb. Basically rig it up so that you can pull a fuse, and then install the bulb across the socket pins. If the bulb illuminates, that tells you that something is drawing current across that circuit. Use a low wattage bulb so it will be sensitive to even slight current draw. The brighter the bulb, the greater the draw, but it might be barely enough to warm the filament.
Lastly you can just pull a relay and leave it out for a couple of days to see if the current draw stops. But that can take a long time.
Once you find which circuit is causing the current draw, then you have to find which device is at fault. That can be difficult, or easy, depending on the circuit.
Be aware that these trucks have non-service replaceable relays in the under dash Central Distribution Block, and it could easily be one of those. I'm not sure how you would test that yourself, and if it is one of those you have to replace the entire block.
All this is assuming you really do have a drain, and not just a weak charging system or battery. Hopefully you have already had that system fully tested.
A couple ways to isolate the problem are -
Remove fuses one by one. Each time you pull one, listen for any clicks that might indicate a relay or device that was powered when it should not have been. Pull relays doing the same thing. A helper with sharp ears (SWMBO) under the dash or under the hood while you pull them is helpful. Be sure to listen for clicks as you replace each one as well.
You can also rig up a test light with a spare 12V bulb. Basically rig it up so that you can pull a fuse, and then install the bulb across the socket pins. If the bulb illuminates, that tells you that something is drawing current across that circuit. Use a low wattage bulb so it will be sensitive to even slight current draw. The brighter the bulb, the greater the draw, but it might be barely enough to warm the filament.
Lastly you can just pull a relay and leave it out for a couple of days to see if the current draw stops. But that can take a long time.
Once you find which circuit is causing the current draw, then you have to find which device is at fault. That can be difficult, or easy, depending on the circuit.
Be aware that these trucks have non-service replaceable relays in the under dash Central Distribution Block, and it could easily be one of those. I'm not sure how you would test that yourself, and if it is one of those you have to replace the entire block.
All this is assuming you really do have a drain, and not just a weak charging system or battery. Hopefully you have already had that system fully tested.
