Battery draw on 2004 996:
 

I know that there is a 996 forum here but I've heard that it's not very active and of course nearly everyone seems to at least lurk here once in a while. 2004 996, (GT3 if it matters), has a draw or dead short while parked and can't seem to track it down the easy way.

We tried pulling each fuse with the test light hooked up between negative battery terminal and cable, it flickered slightly for a couple of them but never went out. Usually in my experience with many different vehicles, the light will extinguish once the fuse/circuit that has the draw is disconnected.

Any ideas? TIA as always.

I think you really need a multimeter. Which circuits flickered with the test light?

We have multimeters. Not sure what circuit it was because the legend for the fuses it missing on the plastic cover but none of them extinguished the light.

Ignition switch? pretty common draw/failure on them
Make sure it "snaps" when you pull the key and locks the wheel
if not change it Change the mechanical and electric part of the assy
Local shops should be pretty familiar with the job

I don't understand how the light would go out.

I am not arguing, fighting, being condescending or an a-hole or nuttin like that.

In my wee brain I picture the negative cable removed from the negative terminal. A simple test light connects the cable to the terminal. The light is on because volts/amps are going through the test light.

I can't see a parasitic draw causing the current to cease flowing.

However, I have never tested draw in this manner. Always with the fused part of a MM.

No fuse usually?

Can you hook up the multimeter outside of car between battery and cable, setting for amperage and lock it up, keep an eye when and how much current is drawn. I have seen glove box lights on other cars stay on intermittently.

Pretty lengthy video here...but worth the time. Denis, measuring milliamps with a multimeter is probably your best bet.

<iframe width="1268" height="713" src="https://www.youtube.com/embed/6xFo_oHFF48" title="Which Parasitic Draw Test Method is REALLY the Best?" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

I'm gonna put my money on it being a bad diode in the alternator.

Great suggestions, thanks to all! Dan, I had read about people leaving the key in and it draining the battery…seems weird but that’s how they are, I guess. I suspected either the ignition switch or alarm because it does not seem to be anything fused.

Repeat the test with a multimeter. The test light isn’t the right tool for the job.

How many amps or milliamps are showing, or how many days for the battery to go dead? Something else to check, this was on a UK site where the starter motor was somehow leaking current to ground, strange but easy enough to check.

Anything plugged into the cig lighter?

Could be many things...but reading amps is the key.

my 996tt always had a drain that would kill the battery after a month or so when i'd not driven or started it. all the research i did on rennlist said it was just part of the quirk.

Not many cars I've owned would start after a month of sitting without a battery tender.

stop. even after a month or so I could get my carb'd aircooled cars started in no time with a decent, years old battery. it has to do with the computer drain that's continues every hour you are awake, every day, every minute. sure, keep it on a trickle, but the OP did not offer that...

Yeah, my 2010 Jetta TDi was left in my garage for something like 8 months in 2020 and it started as if it was driven the whole time. Just, “vrooom.” :)

The GT3 is on a trickle charger all of the time, (rarely driven), but if it’s not, it goes dead. I know that a multimeter would tell me exactly how big the draw is but the test light will tell you *where* it is, which is the info I need.

That's the caveat.

You must use a multimeter, set to low amps scale, in series with either positive or negative post / cable end. The car needs @15 mins after shutdown and locked to go to sleep. So you'll need to find the front hood light switch and close it. It may be in the latch mechanism.

Then disconnect either lead, connect your meter. It should not exceed 50 miliamps. Actually that car may be closer to 35 miliamps maximum. If the draw is within these limits, it's your battery. Using a test light to check for draw is misleading as it takes only a few miliamps to light the bulb brightly.

Lastly if you suspect a bad diode in the alternator, check for A/C voltage bleed when it's running by connecting your multimeter across the +/- posts with the scale set to A/C. Any reading of A/C voltage is confirmation of a bad diode / triode bridge.