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Folks. Am new here so hi and Happy New Year and looking forward to helping and being helped.

I have had a significant battery drain for 3 years. Killed a battery which Canadian Tire replaced and now I disconnect a terminal every night. I was doing some work and through chance discovered that I had 12v + at the compressor housing. Odd on a negative ground vehicle. I connected a voltmeter positive lead to the compressor housing and negative to the negative terminal of the battery. It showed +12v. Thinking I had a short in the alternator which then transferred to the compressor housing I disconnected the positive terminal and it STILL showed +12v. So now I have the battery completely disconnected and when touching the compressor case with + multimeter probe and negative battery post with - probe it STILL shows +12v and a draw of .49 amps.

This is all with engine off and nothing connected to the battery other than the negative multimeter probe. Has anyone heard of this? Is my Jeep possessed? I thought you could not get a voltage or current flow without a closed circuit. I also reproduced this with two different voltmeters.

Thanks in advance.

migrated from electronics.stackexchange.com Jan 13 '18 at 2:34

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  • Is it possible that someone has fitted a second battery to the Jeep? it's not unknown for people do this on 4x4s. – Simon B Jan 13 '18 at 0:23
  • I don't know anything specific about Jeeps. But you are doing what all of us do when something like this is happening -- track it down by narrowing down the possibilities. It's possible, for example, that there is an area that rusted until it formed a low impedance bridging path that would support half an amp even when things are off (though that isn't too likely, it is possible.) Just keep disconnecting stuff until you find the culprit. Voltage is fine to be present, just so long as there is no current drawn from the battery. So focus until you disconnect something that stops the current. – jonk Jan 13 '18 at 0:29
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    if you measure voltage between a "completely disconnected" battery and anything else your volt meter is broken. If you are convinced of this you should physically remove the battery and then try. – agentp Jan 13 '18 at 13:47
  • I have had the Jeep since new so no second battery. Thanks though. – Kevin Toone Jan 13 '18 at 19:29
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Well you definately have something wrong there, I would have to guess something in the engine electrical, like the alternator or voltage regulator shorted out and it took out the fusible link from the engine to the ground. Since the engine is not grounded, you are seeing the 12V that is charged up by the ignition circuit.

  • That sounds very plausible. Will check tomorrow and report back. Thanks! – Kevin Toone Jan 13 '18 at 3:11
  • Coil is disconnected, battery is disconnected and sitting on floor on rubber mat. Still getting current and voltage from frame to negative terminal. This is making my head spin. It is an open circuit! – Kevin Toone Jan 13 '18 at 19:30
  • it has to be a bad regulator inside the alternator, what's your reading under a load on the alternator and with no load – user38183 Aug 11 '18 at 11:47
  • You could have an auto parts store test it, or you can take it apart and test the diodes or you can just buy a regulator and step all over that one you have for a couple years – user38183 Aug 11 '18 at 11:52
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    Does the car have an alarm system? – Steve Matthews Nov 9 '18 at 10:27

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