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Electrical Circuit Drain Test
#1

I recently purchased a '92 968 that had been sitting unused for 11 years (20k miles). After performing the usual set of maintenance procedures, the car started and ran beautifully. I installed a new 7 year battery but after sitting for a few days, the battery was dead. I recharged the battery, disconnected the negative cable, attached a circuit volt tester between the negative cable and negative post on the battery and found a drain. By disconnecting fuses, one at a time, I found the interior/hood/luggage light fuse was where the drain was coming from. From there I found a bad door switch. I thought the problem was solved.



A long preamble to my question. Now, when I attached the circuit tester from the negative cable to the negative post of the battery, I get a brief flash of the bulb that immediately goes out. It does this every time I connect the circuit tester. Almost like there is still a residual drain, but not enough to light the circuit tester. If I leave the circuit tester connected, the light stays off. Any thoughts?
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#2

Perhaps it's your starter cable - not uncommon... here's a link to another thread about it.



http://www.968forums...post__p__118708
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#3

I leave my hood light permanently disconnected. It's like a fridge light, hood open - light on, hood closed - light off? I think when you close the hood Schrödinger's cat is trapped inside <img src="/forum/images/smilies/968/blink.png" class="smilie" alt="" />
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Dave



'93 968SC Nachtblau Metallic Coupe

'89 944 S2 Zermatt Silber Sold

'87 944 Silber Rose in colour only Sad Sold
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#4

Same here, hood light is disconnected.
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#5

Thanks for the tips. The drain in the lights was traced to a defective switch in the drivers door. I also disconnected the hood light. The very slight draw, I am told, is normal and a result of the "computer." That will normally not drain the battery, but if the car is left sitting for long periods, a battery maintainer is recommended.



I have owned some other Porsches, and this Forum is wonderful --- Thanks



jjp
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#6

JJP, I changed out my hood light bulb to a LED festoon bulb from SuperBrightLEDS.com because I usually leave the hood open for a while after a drive to let the engine cool down. You might consider this as well.
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1988 Carrera Marine Blue Metallic 
1994 968 Iris Blue 
2006 Jaguar XJ8L British Racing Green (35k mi)
2002 Ford Thunderbird, Whisper White 
2016 Ram Limited 1500 EcoDiesel 
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#7

I bought a 94 with 17K on her, and am seeing the same slow (very slow) drain on the battery, so I suspect the folks are right about the computer or alarm system causing a slow pull on the battery... mine will last about two weeks with no attention... I could probably do better with a fresh battery, but I chose to go the Charger route, and it works perfectly...



I actually bought a Charger from BMW on ebay for $30 bucks... I like it because it connects thru the cigarette lighter plug, so easy to use and does a perfect job.

I think the same outfit make one branded for Porsche, but the interals are probably all the same....
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1994 968 Coupe, Red / Cashmere/Black, 6 spd, [acronym="Limited Slip Differential"]LSD[/acronym], Part Leather, Alpine, Hidden Radar, Airbox Mod, early Engine Decore Panels, more to come!

2002 MB Silver Arrow SL500 AMG Pack, one of 750 imported.

2008 SX4 Sport, 2004 GMC XUV, 1997 Towncar, police pack sleeper.
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#8

Spent two weeks trying to determine why the battery was going completely dead after sitting for 48 hours. First thought it was a bad battery, so replaced that. Then it looked like the glove box light was not turning off, so replaced the switch. Neither one was the problem. Finally, I noticed the hood light which illuminates the engine bay was not turning off after the hood was closed. The only way I could see this was in the garage at night when it was completely dark. I had to look closely, could see a little light coming through the small gap between the hood and the front body section. So, as posted above, I also disconnected the plug from the hood light. Evidently a common problem, so if your battery is going dead for no apparent reason, definitely check this first, it's easy to do.
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#9

Both my Porsches drain the battery and I have no bulbs in the hood light. If I don't disconnect the battery it is dead in a week. I have no idea.
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92 968 cab (cobalt blue/black top/grey int)

87 944S

19 Audi A6 3.0T

03 Toyota Tundra

 
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#10

if you have a removable face plate in the stereo, remove it. those usually have a pretty high drain
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94 Midnight Metallic Blue Cab Porsche 968 w/deviating cashmere/black interior and WAY too many mods to list - thanks to eric for creating www.968forums.com



"It isn't nearly as expensive to do it right as it is to do it wrong."
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#11

I have experienced the hood thing as well. Hood closed - minimal drain. Hood open (light off - it is only on when parking/headlights are on) there is a noticable current drain. I suspect it is related to the hood switch not the light bulb - perhaps associated with the alarm module. Battery gets low after about 2 weeks with hood open, no issues with hood closed.
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