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exitwound's Avatar
 
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Parasitic Battery Drain Found! How to Fix?

I finally got my ammeter working again, thanks to a $0.59 fuse.

The base drain on my battery was reading 97mA on the 200mA scale.

I started testing the relays and the fuses one by one until the drain was found. Here are my findings:

The Relays
I pulled one by one, testing the drain on the battery with each removed. None pulled had ANY effect on the battery drain.

The Fuses
I pulled one by one, starting at #1 and heading down the list.
  • When the fuse for my amp and bass cannon was deleted, the drain fell to 81mA.
  • When the fuse controlling Central Locking Mechanism was deleted, the drain fell to 80mA.
  • When the fuse controlling Interior Lights, Cig Lighter, Tailgate was deleted, the drain fell to 60mA.

I have recently changed out my hatch struts with new ones. At first, the interior lights would not trigger correctly with the hatch open or closed. I had to adjust the contact point to hit at the precise time of closure so that the circuit would complete properly. The adjustment point I am referring to is located in the lower shock on the left in the following picture.



The trunk and dome lights operate properly with the hatch open and closed. My question is what is continuing to drain on this circuit? The starting issues (dead battery after sitting) occured shortly after I swapped the hatch shocks.

I have pulled the fuse and my interior lighting has stopped functioning. I assume the rear defrosters will no longer work either.

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Black 1986 944
Old 02-04-2008, 11:49 AM
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What about the radio? It shouldn't make much of a difference, but you never know.
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Old 02-04-2008, 12:12 PM
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The central locking area is probably normal. The light problem is probably one or both of the door switches that turn the interior lights on and off. I would suggest taking them out and unplugging them and see if the drain is still the same. If that stops the 20mA drain, then replace the door switches. If it is, then keep unplugging things in the circuit until the drain doesn't cause that much of a difference.

I'm am far from a stereo expert, but should your amp and bass unit suppose to be wired with them having power with the key off? Shouldn't that only have power when you have the key in the accessorie or run positions? I know the stereo should have power all the time on certain leads to keep things like station presets but I wouldn't think you would want that for the amp or bass units.

When you fix those problems, then it should be around 60 or 70 for a drain number and that is about right IIRC.
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Last edited by Razorback1980; 02-04-2008 at 12:50 PM..
Old 02-04-2008, 12:46 PM
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I dont think the radio is the problem. but you never know if it isn't stock or what a PO might have done.

Most radio's will have some drain (very little) that keep the station memory, clock, etc. But any amp, cd changer, etc, should be wired to key on.

Alarms are another thing that are always constant as well, but I dont think he has one installed.
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Old 02-04-2008, 01:48 PM
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This is the first time I've come across the drain from the amp and cannon. They're wired to only turn on with the key, as they do. I do not know why they are draining power with it off, as there is no 12v signal on the remote lead to either of them without the key on.

i will remove the switches tomorrow if possible and report back.
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Old 02-04-2008, 02:05 PM
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The door switches can be a pain. The screw head is pretty small.

You amp definatly shouldn't be pulling any power with the key off.
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Old 02-04-2008, 02:14 PM
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I had a problem like this when I first aquired my 944. The better way to troublshoot is with an Ohm meter across the battery terminals with the battery removed from the circuit. The resistance should be around 20k Ohm if there is not a short or drain. This is form the clock and computer. If it is much lower then there is a short somewhere. If so eliminate or disconnect different items from the electrical system until the resistance changes to a higher amount. Start by eliminating each of the positive battery leads that connect to the battery. Most lilkely the one with the lower reistance will be the one leading to the fuse/relay panel. With the Ohm meter connected start popping fuses and relays one at a time until you find the culprit. Likely it will be a bad relay.
Old 02-04-2008, 02:17 PM
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Look into your car when its dark. I have seen something simple like the glove box light or a small interior light left on draining the battery.
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Old 02-04-2008, 04:12 PM
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the door switches take a small phillips screwdriver, it ain't rocket science.

a 97ma drain isn't bad when clarks references 65ma....+32ma is nothing.
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Last edited by bearone2; 02-04-2008 at 05:08 PM..
Old 02-04-2008, 05:05 PM
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ma draw 94 968

Was getting a 160ma draw. Pulled fuses and found #39 Radio Booster to be the problem. Has an aftermarket radio so it may have the amp and or radio wired incorrectly. Easiest way to test for draw is pull (-) off battery, set multimeter to amps (10-20a whatever your tester has) and connect leads between (-) cable and (-) side of battery. Start pulling fuses until the amps read 0.00

Last edited by DaytonCarCare; 01-10-2021 at 06:35 PM..
Old 01-10-2021, 05:52 PM
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I had a similar issue many moons ago. I had a partial short in the little plastic cargo area light unit. Was staying on with doors shut but somehow was shorting and not lighting up. Check switch on it. Just a thought.

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