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Old 01-26-2019, 09:12 AM   #1
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Finding Parasitic Drain

Hi all:

I'm trying to chase down parasitic drains on my '01S 986 and my '87 951. The procedure as I understand it is:
  1. Turn all electrical items off and take key out of ignition
  2. Disconnect ground terminal from battery
  3. Measure current between ground terminal and negative battery post
  4. If current draw is less than 50 ma, the parasitic drain is normal
  5. If current draw is greater than 50 ma, then pull fuses 1 by 1 until the current drops, which will isolate the circuit where the drain is taking place
  6. Look through wiring diagram where there might items causing the drain, e.g. a switch, etc.

Here's the issue I'm facing. When I try the procedure on either car, I never see any current. This is true even if I turn on one of the systems like the parking lights. Anyone have any suggestions as to what I might be doing wrong? If I can measure a current even, then I won't be able to chase down the drain.

Thanks

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Old 01-26-2019, 10:16 AM   #2
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Quote:
Originally Posted by thom4782 View Post
Hi all:

I'm trying to chase down parasitic drains on my '01S 986 and my '87 951. The procedure as I understand it is:
  1. Turn all electrical items off and take key out of ignition
  2. Disconnect ground terminal from battery
    2.5. Use a jumper cable to connect the battery post to its cable. Turn the ignition on, then back off. Connect your meter probes to the negative terminal and cable, make sure the meter is on and set to at least 200mA, then disconnect the jumper.
  3. Measure current between ground terminal and negative battery post
  4. If current draw is less than 50 ma, the parasitic drain is normal
  5. If current draw is greater than 50 ma, then pull fuses 1 by 1 until the current drops, which will isolate the circuit where the drain is taking place
  6. Look through wiring diagram where there might items causing the drain, e.g. a switch, etc.

Here's the issue I'm facing. When I try the procedure on either car, I never see any current. This is true even if I turn on one of the systems like the parking lights. Anyone have any suggestions as to what I might be doing wrong? If I can measure a current even, then I won't be able to chase down the drain.

Thanks
The reason for 2.5 is that when you disconnect the battery, many systems will not be active again until you connect the battery and turn the ignition on. I had the same issue with my old Dodge.
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Old 01-26-2019, 11:14 AM   #3
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Thanks particlewave.

Well, I tried your suggestion and still no joy either on the 986 or the 951.

When I disconnect the jumper cable, everything seems to go dead. I'll check the multi-meter once again to make sure its capable of reading DC current and I have the probes inserted correctly. I'm pretty sure I do.
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Old 01-26-2019, 11:25 AM   #4
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Yeah, sounds like no continuity through the meter. Either bad probe/wire, connection, setting wrong or the meter may have a blown fuse (meters usually have a fuse or two for the current setting).
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Old 01-26-2019, 05:22 PM   #5
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There is a guide to what the battery drains should be (after all, those remotes must work, right) even a chart of how the drains change over time and how to check them here. Ignore the list of batteries, it is somewhat outdated. But the basic testing techniques are the still the same.
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Old 01-27-2019, 04:31 PM   #6
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Hi all:

FYI: George from 944 Ecology sent this link. This procedure seems much simpler / easier than the one I suggested.

https://www.youtube.com/watch?v=lRcj1fQcWwU
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Old 01-27-2019, 04:43 PM   #7
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I always wondered if a clamp on DC ammeter is sensitive enough to help with this kind of troubleshooting.

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