Parasitic draw

Head Lice

TJ Enthusiast
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Oct 23, 2016
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721
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The land of 'salmon & grizzlies' ....... BC
Have an odd electrical problem with my '04 Sport. It's stock with factory AC, fog lights, and 7 speaker radio option. No electrical 'add-on' accessories or modifications. Alternator does its job. No burnt fuses.

When this vehicle has sat for a week or two, the battery is completely flat. Last instance was a two week sitting period with a voltage reading of 1.5v.

This is the second battery that has been ruined.

Any thoughts on this problem would be greatly appreciated.

Thanks
 

Daryl

2004 Rubicon
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Apr 29, 2018
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1,570
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Earth 🌎
Check for a parasitic current draw.
 
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Swamp Yankee

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Jun 16, 2019
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Massachusetts
Get a inexpensive test light, remove the negative battery terminal, put the test light between the battery and the cable you just removed, if the test light lights up with everything off you have a draw, even if the bulb is dim.
Now start removing fuses first, if the light goes out you have a issue in that circuit put the fuse back in and start disconnecting harnesses and components to find the problem.
If pulling fuses doesn’t make the light go out remove relays one at a time, again if the light goes out you will need to follow that circuit, it could be a relay stuck closed so swap with a known good one before chasing the circuit. Also disconnect the alternator to make sure it is not the issue as mentioned previously.
There are some fancy new circuit test lights out there, I’m not sure they will work for this procedure, I use what I know that’s why I suggested the bulb style test light. The bulb won’t glow with the milliamperes that radio and computer memory’s draw.
Remember there are exceptions to every rule and always use KISS, keep it simple stupid. Speaking of which how many volts is the Jeep charging at with everything off and at 1500 rpms, if It’s a high voltage reading it could be cooking the battery, causing it to discharge on its own when sitting?
 

dbbd1

go away...
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Jan 4, 2019
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1,133
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Oregon
I would only add to the above that there may be more than one circuit creating your problem.
 

Rubicon John

Member
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Mar 12, 2020
Messages
65
Location
Atlanta
The easiest way I have found to find what circuit is causing a draw is to get a voltmeter, switched to 12V DC obviously. Once the vehicle is “sleeping” (Not sure if a TJ does this - just make sure the door switches think the doors are closed, all lights off, etc.) take the meter and probe each side of each fuse. You will notice fuses have a small metal contact when they are plugged in, on each side the number.


Take your positive probe and apply it to one contact, take your negative probe and apply it to the other contact. The reading on your voltmeter should be 0.0 volts. If you see ANY voltage at all there is current passing through that fuse.

You may see 0.1 or 0.2 on a couple circuits such as the radio.

Let me know if you need to get more in depth. I’ve tracked down draws on dozens of luxury vehicles with all sorts of electrical systems.

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