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Discussion Starter · #1 ·
So like the title says, I have a ghost parasitic draw that I've literally been chasing for years...yes, years. (not on my Foucs. 2002 IS300...but have given up on other forums)

Just replaced another battery this week that's completely toast and won't even take a charge. This parasitic draw, when it occurs, is so strong, it'll zap the battery overnight and have even seen it suck down to 5-6 volts left on the battery the next morning. I thought I had it cornered at one time a little over a year ago. It was happening randomly, but frequently. Never could find anything left on. Then the alternator went bad. Replaced that and the ghost parasitic draw disappeared for quite some time. And now the little bugger is back. Killed a battery last week. New battery in last night. Did a test and drawing 30 mA; perfectly normal. Alternator is good; showing 14-15 V at the battery when car is running.

So how do you run down something like this? It's not draining right now with the test, so it may go six days before it happens again or it may go six months before it happens again.
 

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My buddys mom had this issue in a older xj6. Her stereo would come on randomly at night draining the battery over time. Might stick a camera in the car for a few days and see if you catch anything.
 

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So like the title says, I have a ghost parasitic draw that I've literally been chasing for years...yes, years. (not on my Foucs. 2002 IS300...but have given up on other forums)

Just replaced another battery this week that's completely toast and won't even take a charge. This parasitic draw, when it occurs, is so strong, it'll zap the battery overnight and have even seen it suck down to 5-6 volts left on the battery the next morning. I thought I had it cornered at one time a little over a year ago. It was happening randomly, but frequently. Never could find anything left on. Then the alternator went bad. Replaced that and the ghost parasitic draw disappeared for quite some time. And now the little bugger is back. Killed a battery last week. New battery in last night. Did a test and drawing 30 mA; perfectly normal. Alternator is good; showing 14-15 V at the battery when car is running.

So how do you run down something like this? It's not draining right now with the test, so it may go six days before it happens again or it may go six months before it happens again.
Any aftermarket electrical devices installed?

With a multimeter, start pulling fuses one at a time while looking for a draw. Dont forget the fuse block under the hood.

The fuse with the draw is the circuit you need to sort out. So you will have to cross reference it with a shop manual to determine where it goes, and what components are actually on it.

Besides that, I'd make sure ll the grounds are clean and tight, same with battery cables.
 

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^ this

but keep one thing in mind, you will want to wait until off of the cars modules "fall asleep" before taking any readings. also pulling some fuses may cause modules to "wake up" and you have to wait again. most modules take anywhere from 15-45 mins to fall asleep.
 

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I say this every time I hear about electrical issues that make owners want to call an exorcist:

Grounds. Grounds are the devil, and the bane of every electrician/electronics technician. Bad grounds can cause more, and more varied problems, than any other single problem source, and by a lot.

My sister's car had an intermittent cylinder 3 misfire on a Honda Civic for years, and every mechanic in her town spent months (and $$$$$) replacing all manner of parts and testing and troubleshooting... I replaced all three grounding straps (engine to body, transmission to body, body to battery) and the problem disappeared for good, along with about seven other problems she hadn't bothered telling me about because she'd given up on them ever getting fixed. The cables were green and nearly disintegrated. The engine also gained about 20hp because the spark wasn't randomly blowing out because it was so weak.

Now I know you're wondering how bad grounds can cause a battery to go dead, but I assure you it's possible. Bad grounding can cause modules to misbehave and turn on. Bad grounding can, bizarrely, cause high current drain (especially on sensed circuits that kick up the current draw because it's not seeing enough current through the circuit because of... you guessed it, bad grounding).

My recommendation to you is to replace all of the major grounding cables in your engine compartment with brand new, preferably marine-grade, grounding cables. While you're in there you might consider replacing the "Big Three" cables (battery-alternator, alternator-starter, starter-fuse block) with bigger-than-factory (I recommend 0-gauge at least) cables. Make sure you size the ground cables to match - there's no such thing as too big (physical space permitting)!

Even if it doesn't solve your problem, and I can't guarantee that it will, it will remove a great number of variables and improve the overall electrical health of your vehicle (and engine) immeasurably. Once you are sure your grounds are good, then you can start getting into component-level wiring (cut/shorted wires, etc.), which can be an endless rabbit hole. I recommend pulling 50% of your fuses and leaving overnight for three nights - if the battery is good, do the other 50%. Once you find the bad half of the fuse block, pull 50% of those, and keep going down that way until you isolate the fuse (or fuses!) that supply the faulty circuits.

Good luck...
 

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Discussion Starter · #6 ·
Thanks hawkeye, and trust me, I totally get the grounding issue. Had actually already thought of that. Currently inspecting my grounds in the middle of other projects while the car is torn down. Not discarding this advice, but the random dead battery is literally the only symptom. No other electrical gremlins on this car at all. No corrosion or bad looking (ground) wires that I have seen yet. I don't think the fuse technique is going to help me because if you reread the post, I do not have the problem every day, nor every few days. It is completely random and once in a blue moon. Car has been sitting for two days now and it's still just pulling a nice steady 30 mA.
 

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Any aftermarket electrical devices installed?

With a multimeter, start pulling fuses one at a time while looking for a draw. Dont forget the fuse block under the hood.

The fuse with the draw is the circuit you need to sort out. So you will have to cross reference it with a shop manual to determine where it goes, and what components are actually on it.

Besides that, I'd make sure ll the grounds are clean and tight, same with battery cables.
^this is exactly where I would start. You will find it
 

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I would find it if I could catch it when it has the excessive draw.
this is key, part of what makes finding a problem like this on modern cars is that it is often an intermittent issue. if its not constantly draining, it could take a long time to find the issue.
 

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Im not intrisically familiar with a 2002 is300 electrical schematics, but on cars that have a CAN netork, there are dataloggers that can monitor for bus wakeup. This is pricey equipment and usually found in dealerships. I have actually had to keep cars for a week to reproduce a intermittent bus wake up event, fyi.

Without something like this, the best way to begin is to see how many milliamps its drawing when its acting up. That may actually help narrow it down.
 

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Discussion Starter · #13 ·
Well since my occurrences with this problem are completley random, heres a hypothetical question...

If/when it occurs again, is ther anything i can do 'at that time' to try and pinpoint the culprit? Im not going to catch this until i go get in the car one morning and the battery is dead. Anything that can be done at that point? But disconnecting the battery will most likely trigger a reset and itll dissapear again anyways.
 

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Here's what I'm reading here; you have an intermittent current draw, a big one. If your car is killing a new, fully charged battery overnight, that's amps, not milliamps. And in your case, it's intermittent, and those electrical issues are a huge PIA to track down.

So, your car has a fully charged battery. You turn it off, turn everything off, lock the doors and walk away. Sometime, in the middle of the night for reasons unknown, something suddenly either turns on (and whatever it is, it's drawing big power, like your electric cooling fan) or some sort of short to ground. So it got me thinking. What if you could rig up something that when that gremlin comes back, you're alerted to it, like a loud ass car horn?

You know the parasitic draw trick where you put a 12V auto light bulb (instead of a milliameter) in series with the battery's negative post and ground cable? What if you wired a car horn there instead? It wouldn't power up until a massive current draw appeared there. You'd need a typical 30A relay, because a car horn draws enough current that relays are typically used.

IMG_5574.JPG

Will this work? I don't know. I'm just thinking out load. But if it does, you'll know about it, and your neighbors too. At that point, you'd know your problem is there, and you could swap out the horn/relay rig for a milliammeter.
 

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Discussion Starter · #15 ·
Steve...your second paragraph was spot on.

I like, and totally get, your horn idea. I don't fully understand how a large draw would kick on the horn though. I've never heard of doing the light bulb in series with the ground cable to check draw, only a multimeter. I don't see how the draw would turn the light on in this configuration.
 

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Interesting problem. Just some ideas to get you started.

One way is to convert current to voltage. It's very easy to measure voltage with something like Arduino, Raspberry Pi, or perhaps a cheap DMM (and hack it to osund an alarm or something). Two ways I can think of on converting current to voltage: current shunt and hall effect sensors. Current shut is probably cheaper, but problem its output is in tens of millivolts and most ADCs measures in spans of 1V-5V. So you'll need to amplify the output to the range of the ADCs. Anyway, the idea is to write your own code (or there might already be some public domain ones you can use) for Arduino or Raspberry Pi to measure this voltage and then when it's over some trigger voltage (current), turn on a DC output to sound an alarm or something. The Arduino and R.Pi both have everything you need to do that. You just need to supply the shunt or hall effect sensors and the buzzer and write your own code.

Hall effect to measure DC: howto?
ARCHIVE: : Hall effect sensor circuit diagram
reading mV
https://www.amazon.com/gp/product/B...9-399c-49e1-901a-7b8786e59436&pf_rd_i=desktop
https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=aps&field-keywords=current+shunt
 

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Since you said that when it happens, the voltage drops down to 5V? If that is the case, then maybe it's simpler to just drop the 12V battery to ~5V with a simple 8K/10K voltage divider like this. R1=10K, R2=8K

[+]---R1---x---R2---[-]

Connect the + batt to [+] and - batt to [-]. And measure the junction marked 'x' with the Arduino's built-in 5V ADC and if it drops more than say 2 or 3V over night, then activate an alarm or something. Or you can monitor the voltage once every 100 mSecs (or once per second something like that) and if it drops more than some threshold, sound the alarm.
 

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Steve...your second paragraph was spot on.

I like, and totally get, your horn idea. I don't fully understand how a large draw would kick on the horn though. I've never heard of doing the light bulb in series with the ground cable to check draw, only a multimeter. I don't see how the draw would turn the light on in this configuration.
The older trick (instead of using a DMM) was to just put a 12V lamp in series with the battery negative post and the negative cable. It did the same thing an ammeter would; indicate current flow. The negative post in this case of an intermittent current draw, would now be more positive with respect to the ground cable, or a difference in potential. The bulb wouldn't show how much current like an ammeter would of course, but would indicate current flow. You'd just put the 12V lamp in series, and if it lit up significantly (not a very dim glow) you'd start pulling fuses until the light went out. When it did, you'd just found the faulty circuit.


I pulled this pic from the web. In this pic, one of those very simple circuit testers was used. The bulb is inbetween the battery negative post and the neg. cable (the tester's alligator clip lead is on the disconnected negative cable). The bulb is brightly lit, so something is on; got a door open/ignition on etc., or a parasitic draw.

I was just thinking that if an intermittent current draw of that amplitude could power up a 12V lamp (which it surely would) why not use something that, instead of emitting light would alert you by blasting 100dB? Those phantom electrical issues are hard to find.

I've tested old car horns by just laying one across a car battery's terminals. I think they draw 5-6A or so, so you could probably delete the relay altogether for this temporary situation and just wire the horn inbetween the neg post and the negative cable. Will it work? I don't know. Only one way to find out.
 
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