You Think  You Have a Vehicle Parasitic Drain(s)?     
(AKA: Dark Current, Phantom drain or Ghost Current , scary huh?)   Jump to a fast test:

These tests, work on cars, trains, boats , planes, motorcycles, or any system with complex wiring.
This page, is not for people that have the battery die and engine stalls, driving to work. (a bad charge system)
You have checked all the below first:
  1. All fuses are good in both fuse boxes. (cab and engine bay)
  2. The battery is charged to at least 12.6vdc and car always runs great and cranks and starts ,when it is  charged.  This 12.6vdc is a charged battery , in warm weather.
  3. The Charge or Alternator failed  lamp in the dash cluster, does not glow, running. nor is idle below 800 RPM , EVER!  See CHARGE failures here.
  4. If the battery drains over night (see below DRAIN) the car jumper cable jump starts every time or you shop battery charger, charges the battery and it starts everytime.
  5. The battery discharges parked, at home or work, and I can't find the reason, see the below DRAIN. (CAR ALWAY STARTS, FOR SHORT PARKING TIMES)
  6. I spent $150 on a new Bosch Battery and the battery still goes dead, parked.  Why do that.? the best meter is only $50.
  7. I parked the car, at night, I then turned off all lights in my garage, I waited, 15min. for my eyes, to adjust to the dark and then walked around the car looking high and low, there is no GLOW.
  8. I put my volt meter leads, across the battery terminals, (RPM 800) running hot engine shows 13.3v to 15vdc, proof that the charge system is working. if not, see charge failures.
  9. Jumper cable , jump starts off  a running donor car , always cranks and starts my car. ( proving the cranking system is ok)
  10. You have DRAIN. You have a Phantom drain. 


I define parasitic drain to be, any drain over and above the factory specified drain limits (they are very tiny , 10s of milliamperes max)
My new car from Jeep ships with the IOD fuses pulled, to prevent normal drains , shipping car long distances.   See safety. So can you , if going on vacation (car left at home) .
In a pinch , just pull the battery negative lug to stop all drains, (no need to pull both, ever) Or buy the Walmart battery department lug cut off switch, installed to the battery NEG lug.
All accessories OFF , lights off , doors closed, Audio systems off, Ignition key in your pocket, but Alarm active?
Keep in mind that your battery may go dead or too low charge, parked for long term, in a few months, if not kept charged.
This occurs due to normal dark current and internal chemistry action of the battery, also called battery self discharge ( even sitting on your work bench)
Factory spec. drain varies from   .010 amps to .050 amp.
The more accessories you have,  the more drain, (radio, power amps, remote start devices, alarms, immobilizers, NAV, {LOJACK  with a bad internal battery?})
If you only have the stock ECUor  PCM / TCM on car,   0.010.    Ten milliamps is spec. normal drain, or less. Less is always great.
Most bad Drains read above 0.10 amps.  1/10th of a Full ampere. Most light bulbs stuck on are that or more.
Some lamps can even draw a full  1 AMP. (brake lights) 1000 times normal drain. see?
Normal drains:
Most lead acid batteries , lose 1% to 5% per month for Lead Calcium batteries. (called freedom batteries)
Add this to normal battery drain of 0.010 amps,  and you can see, after 3 months that a no crank situation happens, after this long.
 No lie, the $10 Walmart meter can in fact measure accuratly this drain.

How to deal with this problem of excess drain?  DIY;
  • Use and ammeter (see the drain and pull fuses to find the branch that has the drain)   ( both old meters (series) and new ampclamp)
  • Use a passive test lamp (best, is lowest current lamp you can find)
  • Do the Dark test, seen above. #7

Buy a $15 meter  (is the best way)
First read the warnings in the end of this document .

All the below, assumes a good battery.  ( you replaced it , borrowed it , or had it tested, ok ?)

Open your vehicle and look everywhere , that's right , everywhere possible!
Skip nothing.
Your car has no lights, or lamps stuck on. ( look at the car in the garage, in the dark )
Please look everywhere , in the dark , let your imagination run wild.  ( trunk , glove box, hood ?)
You  will be surprised  how well this works.
Look for hidden switches or objects, cobbled  onto wiring, with crude splices, on your car. Look for Hacks to wiring!
Trace them, to find out what they are and what they do?  ( look for not original equipment)
The newer the car? the more things that can fail and drain the cars main battery flat.

How to cure the problem.  ( using a simple test lamp) Not the best way, and impossible if drain is 5 times normal. (weak drains happen too)
Begin  diagnosis by making or buying this 12 volt  test lamp.
You can make one, by buying some parts:
Buy a discrete 12 volt light bulb with wire tail leads and alligator clips.  Make a"Test Lamp".
Radio Shack has the parts and you want a light bulb with the smallest current rating.
about 100ma  (0.100 amperes) or less. ( a spare dash cluster warning lamp is very close to ideal)
A 1157  stop lamp is very poor .

It needs a socket to mount it and to be able to mount test leads and clips.
Tell the Radio Shack guy , I want a very low power 12-vdc Lamp and socket.  He knows what to do.
For me , I just solder wires directly to lamps. Grossly simple works here. Nothing fancy, just a low current test lamp of any kind, rated for 12vdc.
Do not use and LED lamp.!

First we do an Obvious test.
Turn off (disable) everything electrical in the vehicle ( Head / running lites, too)
Keys in hand , Ignition switch , not in the accessory position.

Keep in mind that not having  a proper schematic for your car may make this whole job hopeless. solves that. (cheaply and at great quality)

Lets proceed on the blind hope path.
Check all sources for stuck "on" courtesy lamps glowing::
Eg: Vanity mirror lamp,Glove, hood, trunk, foot wells, console, & door jam switch, lamps, or stuck ignition switch or stuck on brake lights.  Suspect bad car clock if it is not a digital type.
Clean out the cigarette lighter socket hole with air or a  non metallic brush. ( did someone drop a dime into this hole? look ! )
My Vitara has a hot at all times (cig power port) and a hot only key on CIG lighter port. (I use the former to use a solar charger , parked at the air port)

No lamps "on",  of any kind ? Nothing is glowing, at all key off.

Remove the negative clamp at the vehicle  battery post.  (marked MINUS)
 Place one lead of the test lamp on the negative post of the battery and the other on the negative clamp lug.
The lamp glows if there is a parasitic drain.
The lamp will be dead, if there is no drain.
I like the amp clamp tester best , because the actual drain value gives me clues as to the cause.
end lamp drain method.
You would then start pulling fuses like a mad man, to find the cause (man or woman). (and last pulling main harness connectors, all over the car body) to find what path the drain follows.
Ok, you have a  phantom drain. ( technically called a parasitic drain)

The EASY way with the  The D.C. Amp Clamp Meter . (Best of best , second best is here)
Just clamp on, measure current key on or off,  no blow fuses, no burned up meter, easy as cherry pie.
Do not buy any A.C amp clamp meters (more common, as 9 out of 10 are...) it will not work.
 I got  mine for $45.  It must be DIRECT CURRENT AMPS, this tool is Inductive pickup type, (no wires)
The tool shows leakage on the low range and the direction.
Sold by MCM Electronics(or Newark E14), it does DC Amp's so easy , its a crime. #72-7224

Best bang for the buck.
My meter must be zeroed first, to get accurate low current readings, the instuctions with the tool, shows how to do that.
"Above meter, turn on to 40a and press REL  button for  zero cal."
OLD slow, but sure way with cheaper meters:
The FAST test with a DMM set up as an Ammeter.   there is no down side here, but 2, drain might hide when the lug is  pulled, (dang) or the meter  fuse is blown)
The Car Igniton key is off or in your pocket (best).
Note that the meter is connected in series with the load (never put this meter leads directly across the battery terminals, in this way or smoke lets out of meter case, or fuse blows in same.)
We use the NEG lug for safety.

In this below photo , replace the Meter (DMM) instead of a above test lamp.
The meter below is on the 10 or 20 Amp Range , follow the manual for connections and dial settings. RTM. read the manual.

Please imagine your TEST LAMP , connected (located) where the yellow meter is , below ! If using a Test lamp.
 I never USE TEST LAMPS! Because I wish to know the true flow, in amps.  The true flow suggest, what is bad (active falsely). (a lamp, short, relay, a VSV, a solenoid or ?) 
Dark current begs to be messured accurately.   (the DMM will correct for the polarity automaticlly )
Some  meters, must be zeroed first, to get accurate low current readings.
If the reading is 0 mA , zero miliamps at all times (tested), then the fuse in the meter is blown , replace it.  and do the test below to test the meter.
Mine reads,  0.013 amps.  (good)
An analog needle meter can be used but  observe polarity.
Any technician will test his meter before conducting this test. use a 100 OHM test resistor ( Radio Shack(tm)  sells them)
For a drain test resistor a 100 ohms  would even be better for a test.  I = E/R  , I = 12/100 , or 120 MA.
To conduct this test ,place the meter in series with this resistor and then across the battery.  ( Click here to see how)
If your meter fuse is blown, this check or  test will be a false reading of  ZERO.   Replace the DMM fuse , now. Yours is blown.
Amp meters, go in series with load or branch load circuits, never in parallel.  ( or the fuse in the meter will BLOW)
When I state LAMP here, I mean the test lamp or any ammeter used.

Phase #1:
Now, at the fuse panel ( you have 1 in the engine bay and 1 in the cab. some cars have 3 panels  or more. read the FSM for your car.)
Start removing one fuse at a time. ( putting them back as you go).  (do not mix fuse colors)
Watch For any decrease in test lamp brightness. (or loss of drain current)

I would start with the radio fuse , then the "Low Jack" fuse , then the CD/MP3 player fuse and amplifier.
And all of  that new extreme Audio equipment what so ever!
Like that satellite/GPS/killowatt mega multiplex monster bridging Amplifiers.
or the new neon under body lighting silly option  and then the Alarm unit.
The more junk on your car, the more problems you are going to have.
Start by unplugging this stuff !
If the lamp goes out, you have found your problem. ( or it dims radically )

After pulling all  these common fuses is done ,  then just pull all the remainder of  your fuses, not tried. (assuming a glowing test lamp)
Didn't find the problem yet?

If you had a  real Amp meter ,then you have already discovered the failing branch circuit.

That is because the meter shows you that pulling fuse X , did not reduce the current one tiny bit.
The amp meter leaves no need to guess, unlike the silly test light, that might be glowing and you can't see it  GLOW !
The meter is vastly more accurate detecting small changes in current !
Use and inductive amp clamp meter for best results.
Measuring for drain below 1 amp, a meter works the best. and for sure below 0.1 amps. (some test lamps do not glow, at low bad drain currents)


That was the easy way.  ( only one fuse pulled, at any one time)
Now we are at phase 2 the harder way.

Phase #2:  ( only necessary if using a silly test Lamp  )

Remove ALL the fuses while watching  your , test lamp, and when you are done all the fuses are out of the vehicle. (do not forget what color fuse goes where !)
( keep notes as to NAME and ampere rating on the fuse, as you take them out, or you may be sorry later)
If you have any After market Electronics on your vehicle , you may find hidden fuses under the dash / hood or trunk.
Find and remove all these hidden fuses too.
Now is the lamp still glowing? ( the amp meter would read greater than 20ma  any more and that is too much. )
35 ma is SAE/ASE spec. (max. drain guide lines.)
(most cars are similar )

If you have 100ma, as may people do , with this problem, then you must do phase 3.

Phase 3:
Remove the red wire from the back side of the alternator ( it is a huge #6 gage,  1/4 thick wire).  (DO NOT LET THIS LUG  HIT GROUND or you blow a huge fuse)
What I do is here,
  • I pull the battery negative lug.
  • then pull the alternator 6 gage wire,  and using electrician tape, I tape this free wire end ,so it can never touch ground.
  • then put the battery lug back
  • last I check for illegal drain, if gone the alternator is bad. (It has bad 3 phase diode pack or excition pack or regulator, new alternator time.)

Did this fix the drain ?, if yes the alternator is bad.
Remove the alternator plug ( 2  to 4 wire connector) , did this cure your drain?, if yes , you again have a bad Alternator.
If I can not find the drain with fuse pulls, I then try body harness connector pulls.
You will find it.

Many Alarm systems were installed by gross hacks.  I have seen many car butchered, by these people.
If  you suspect that the Ignition circuit is drawing too much current ,because only THAT fuse reduced the current to zero, then you must analyze that circuit.
Pulling a fuse and seeing a drop in current tells you ,that this  circuit PATH,. is illegally using current.
This current is excessive.

You might  have to pull your ECU computer to see if the current goes to zero.
If your ECU pulls too much current, then you have a bad ECU (sorry)  (one exception below)
The ECU main relay, must not be energized , key off. So pull the MAIN relay and see if current drops. (It must not drop or the relay is bad)
On some cars the ECU can fail and hold its own main relay energized at all times, this is a bad ECU.
The ECU memory pin always uses , max 0.010 amps or less. It is HOT all the time, key off too.

Working with the ECU requires care, due to the fact, that it is very expensive.  (never short its connections,to ground or to Battery Plus )
  • Pull fuses.
  • Pull connectors, any and all. (even the main body harness hidden connectors)
  • Pull hacked in electronics, no matter what it might be, pull it, disconnect it, pull it's in line fuses.
  • Remove any and all sensors connectors
  • Pull the MAIN relay  and the fuel pump relays.
  • Pull all relays, solenoids and VSV (vacuum solenoids valves) on the car.
  • Doing all this will find the drain, I am 100% sure.

Prevention tactics:
Install  a Battery cut off switch.   $2 at Harbor Freight this week 12/2006.
bad side , it Kills your alarm system.

RV style Diode blocker for an extra battery, that is only used for starting.
You now have 2 batteries, but the non starting battery can be a cheap motorcycle or UPS  battery.
Problem is the extra battery only gets a 90% charge.  See #3.

Voltage sensing relay , a relay with a simple circuit that drops a battery when changing has stopped.
Similar to  the Diode blocker, but will charge both batteries 100%.  ( requires 2 batteries, too)
This  is the best solution to people running Alarms and Log Jacks, etc.
This is what all Boat and RV professionals use.  No fooling around with 1 battery !

Priority start device , a device that monitors STATE OF CHARGE on the battery (1) and then breaks the load when it drops below 80%.
Advantage, is only one battery.
Disadvantage , car may not start up it is very cold and the engine is very big.
Think of 500 cubic inches and Alaska.   (humm, battery goes to 80 , one month later it wont start)
Not too good,  if you have and Alarm , that becomes dead at the 20% threshold of SOC.
Expensive. $70 , approx.
This is not a solution, it is an ace in a hole, and a little cheaper than any 2 battery solution.

 Buy the biggest battery, that will fit in your vehicle and put that in the place of the existing battery.
simple and can work for some people and some cars. 

Any solution the produces a dead accessory battery will cause problems for you.

Newer Radio's,' use Flash memory  (doesn't forget), so maybe buy a newer Radio, ok.
Cheap memory requires a battery , quality $1 more memory does not.
Low Jacks use power while listening, with their monitor receivers.
Buy an alarm system where the main unit can be easily unplugged and one that uses the least amount of power.

You can always, Unplug the whole alarm system ! If you are desperate.

6.) If your car does not already have and AGM battery then update to one , as this battery has less of a self discharge rate and greater energy/density ratio.

Other Solutions:
Put a solar cell panel in the rear of your car to keep the battery charged up ( parked in sun , of course).
Plugs into cigarette lighter plug ( now called a power port).
At home get a trickle charger.
If you park away from power and away from the SUN , then you are SOL (sorry out of luck) , but If I was in that pickle, I'd go for a 2 battery solution.

There is one band aid solution where by you tote around a special battery in a plastic box  that may , jump start your car. 
One is called "Vector Start-It Jump starts System/Power Supply " it's sold on
This some times works and sometimes does not. If the battery was totally drained , it will not work.  ( head lights were left on?)
Oh yes, you must keep it charged or it will be dead too.  ( it has a 17 amp/hour battery inside and is marginal to useless on big cars and trucks)

Do not remove air bag fuses , unless you follow the instructions in your shop manual and by no means do so with people or pets inside your car.
Do not work in FRONT of any AirBag system SQUIB device , without first following the factory instructions for disabling the air bags. !!  <<  DO NOT! 
Battery pull (pull the NEG battery lug first , and put back last or you will be in danger of "acid bath")

If  you remove power by disconnecting your battery, you will lose the memory settings of many devices.
On NEWer Cars, transmission computer (TCM)  may have to re-learn its profiles and may shift roughly, for 1 day. (a few hours) Let it do its thing, don't panic.
The cars engine ECU  will forget Long Term  fuel trim  LTFT and may have less power for a few ,minutes hot engine. ( very slight). Just drive it and don't worry this, but some folks can feel it and worry.
Your Radio may (old cars for sure) forget all it's station settings , forcing you to reset them. A pain, but not a safety issue, Radio works!
(on new cars you can lose RADIO code and NAV codes !)
The car alarm may go goofy , requiring reprogramming.  
In a  shop, they place a regulated trickle charger on the battery leads before removing the battery.
or you  can buy or make a 9v battery device that hooks to a cigarette lighter adapter and you plug it in.
 (its just a 9vdc smoke detector battery and a 1N4001 diode (anode to battery +,  cathode to cig hot pin)

The Collateral battery disconnect issues list.
  1. Lost radio stations settings. (write them down first)
  2. Lost RADIO security code, (read the operators guide for how to avoid this)  this can be a real pain....
  3. Lost NAVIGATOR codes. same as RADIO. (same pain)
  4. PCM (ECU)  LTFT,  fuel trim, forget this. it's not an issue. "LTFT is OBD Long term fuel trim" this self corrects in minutes or less.
  5. Tranny learn mode.  (let it relearn) 15min drive.
  6. On even newer cars with TBW, Throttle By Wire, some need to do re-learn,  Read the FSM on topic. (bad idle RPM or limphome mode until corrected)
  7. There are other issues on newer cars,  other "X- BY WIRE" systems. Electric Steering, etc.  RTM , read the FSM.
  8. Alarms (see the operators guide and FSM, it covers how to reset your alarm, most do so automatically, but not all)

Want to learn something about DC electronics ,then this site is really very good.

My $20 Hoyt SG-1 meter
(hard to find, but can be found using Ebay long term, monitors)  See lots of cheap tools here.
This tool  is INDUCTIVE , NO WIRES !
This tool has two inductive slots in the back, one for starter current and one for alternator, use the alternator side.
Hoyt ?,Finds bad Alternator, bad starter (dead or shorted) and PHANTOMS drains.   I use my AMP clamp meter for drain, mostly.
This meter works good for finding 3 Amp drains or more,e. and not low marginal drains.  For that use the AMPCLAMP.
It does not find small drains well. See the next tool for small (tiny) drains.
I can find any lamp stuck  on, fast with this small meter tool.
Some cars have glove box,console boxes, or  trunk and hood lamps, that can stick on.

There is a better meter and cheaper, that finds low level shorts sold on Amazon, and is more Sensitive. For about 25 bucks.

SG Tool Aid 25100 Short Tester
The tool shows the drain, and direction, it also pulses, and you use it only during the pulse time. 
As you move the meter, along a shorted harness, it will NULL out, this is the point of the short.
See this page for details.

This tool above is hard not to love... love at first sight. (finds shorts and drains) but may not find a drain 5 times over spec.
Keep an open mind many things can leak or have drain, even the Alternator can be bad (works ok mostly) but drains the battery parked.  (amp clamp the alternator big wire to see it leak! 0 amps good)

Safety: PLEASE...
Do not pull the battery Plus lug first. (always last ) last off first on.
Do not let  the Plus lug terminal hit the hood of car (wrong battery used, too tall or adding lug power cutting switches ?, there!)
Do not put the battery lug cutout device  connector on the Plus terminal lug. (use the NEG lug !) for max safety too you.
Do not cross the battery lugs with any tools, ever. (boom acid flies or worse hydrogen bomb (1/2 joking that,the Hydrogen is real and does burn fast' picture in mind flying burning acid baths!)
If compelled to take off the plus lug first (don't) use fully insulated tools for battery work. (sold in stores) ( I've had to work huge UPS 911 power systems that needed battery swaps HOT)
The battery is 12 vdc, it will not shock you.  (nor will the back EMF pulses can hurt ,you if you play (on/off/on) with the lugs key on, but can be felt.) (with key off there is no back EMF pulsing)
The Battery must be connected or disconnected with the key off.
The battery must never be connected backwards  at its lugs. or blow up lots of  nice electronics $$$$$$$$ (yes, some are protected here, but which are?, is a dice roll)
Never run the engine  with the battery disconnected or risk alternator going nuts, (reg) and burning up electronics again.  (we did this long ago with DC generators say in 1960 and no electronics in car) Stop doing this,please.
Do not add loads (new toys, like remote start or? ) to the battery without proper sized fuses. (and a way to turn them off )
Do not get battery acid on your hands (you will) then rub your eyes, DO NOT. Wear gloves or like me, bathe the battery (brush on) with backing soda and water mix.... The battery is now safe.
Do not let a fully discharged battery to freeze, it will crack  in half.  and will be a danger to ALL THINGS, people , pets things near. (leaking nasty ACID)
Do not use mega powerful battery chargers (100 to 300 amps), then turn on the key  and blow up electronics. do not. (and for sure not with a very dead battery !)
Do not jumper cable jump, any battery backwards, or BOOM. (acid bathes are not fun)
If really paranoid?, (lots of valid reasons) charge the battery with the NEG lug pulled, charger neg clipped to battery minus post.  (ignore this for tiny float chargers)
Do not charge a battery backwards.
Do not remove the alternator big 6 gage (say) lug wire (stud on ALT) witht he  battery NEG lug not disconnnected, or BOOM.

By : rev1: 12-2007    rev.2  4/07-2009  V4: 4-14-2014 (add Hoyt meter and one more at end. and revised  greatly)V5. safety added.