Battery Draw on '79 Cutlass Supreme

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Jan 30, 2019
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Hello everyone,

I have a question for you guys. My 1979 Cutlass Supreme Brougham has something that is drawing power from the battery when the car is not running. If I drive the car everyday (which I usually do in the summer as it is my daily) it's fine, and fires up right away. But if I leave it for more than two days, the car has no power whatsoever (won't crank, no lights etc.) and I have to recharge it.

It's defenetely not the battery as it is relatively new and has held it's charge 100% over the six month winter while it was disconnected from the car. I don't think it's the alternator either as the voltage measures right around 14V while the car is running, and fully charges the battery by the time I come back from driving it. I am also certain that it's not any of the obvious things like leaving a light on!

I find it very strange that there is something drawing power due to the fact that there are very few powered features in the car. I don't even have a stereo installed right now. The only thing I can think of is that there is an anti theft (immobilizer) system that has a small red blinking light. I know it wouldn't be the small LED but I'm wondering if there could be a larger draw coming from the immobilizer system while the car is turned off (maybe it's always running)?

Any help or insight would be very much appreciated. The car is in storage for another week, but I'd like to get some ideas so I can try and solve it soon.

Thanks!
 

maxi426

Apprentice
Sep 20, 2018
53
18
Try removing all connections from the alternator while it sits, then see if the battery stays up. The diodes inside the alternator can short, and cause a parasitic draw. The alternator may still charge, but usually at a reduced rate
 
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Max Headroom

Master Mechanic
Sep 8, 2011
369
63
Maxi 426 could be right. See if you still pull 14 v after the battery is charged. If so, the problem could be the regulator system the same parasitic draw is still possible.
I had a short in my dome light kill my battery for a couple of months, before I finally got desperate enough to check it.
Also, be sure that the hot wire for the sound system is not shorted.
 

fleming442

Captain Tenneal
Supporting Member
Dec 26, 2013
13,085
113
While everything is off, put a conventional test line inline with the battery and the terminal. If there's a draw the light will be on. Start unhooking stuff until the light goes out- start at the alternator.
 
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Steve Bakken

Apprentice
Feb 20, 2015
65
8
We just had this exact same problem on my son's '78. Turned out to be the driver's side door jamb button. One of the wires was grounding out just enough to draw from the battery, but not enough to actually turn on the dome lights or buzzer. Pulled it out, wrapped the connections with electrical tape, and the problem was gone.
 
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hangar401

Greasemonkey
Supporting Member
Oct 3, 2019
118
43
Maybe look for short in the trunk light,hood light mine was the domf car sat for days,battery was too low to start the car
 

pontiacgp

blank
Mar 31, 2006
29,389
113
Kitchener, Ontario
While everything is off, put a conventional test line inline with the battery and the terminal. If there's a draw the light will be on. Start unhooking stuff until the light goes out- start at the alternator.

I use that method but I just pull fuses till I find the cucuit causing the problem, then track it down from there
 
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