Hi all
I have a 2005 Mustang GT. About 110,000 miles on it. It's in pristine condition and I've never had any issues with it.
However, suddenly out of the blue, my battery is getting completely drained while it's off.
No lights left on, nothing.
But after a day or two, it's so dead that not even LEDs will glow.
After charging it back up, I check around for a culprit but come up empty handed.

Are there any common things on these cars that could be the cause?
Otherwise any ideas where to start?

I'm good with electronics and wiring but have never had to track down a draw before.
Thanks

 

We Have Tons of Threads on This Issue. So Much To The Point of Where Do I Start.

Moved You To Proper Section!

Realize I Like To Answer Some Threads in a Broader Context In That I May Address Things That are Not Your Particular Issue But Maybe Useful To The Next Reader.

Well Today I'm Going To Start With The Basics. Because I Just Went Through This on My F-150. In it's Case it Was an Internal Short in The Battery Due To Age. Charge it Up It Starts and Let Set and it Was Dead Again. So First Things First Do a Test on The Battery to Check For Cranking Amps after a Good Full Charge To Make Sure it is in Good Condition.

{NOTE} While The Older a Battery The More Suspect it is For Internal Drain, which is Caused By Contaminants Shorting The Plates Inside it Can Happen at Anytime as They Are Just Floating Around inside Battery. A Crank Test Will Tell The Tale.

I Recall over The Years Working at The Various Dealerships We Would Get New Cars That Sat on the Lot For a Long Time and The Battery Would Fail Before The Car Even Sold or Shortly Thereafter. Car Batteries Hate Sitting!

If You Don't Have The Equipment Many Parts Houses Will Test Batteries and Check Codes For Free. While You Are At it a Good Code Reader Which Could Check For any Codes {ALL CODES NOT JUST P-Codes} at All Would Be Useful. If Battery is Going Completly Dead in a Short Period Codes May Get Cleared So May Need To Put Some Drive Time on Car Before Checking For Codes.

So If We Rule Out Just a Battery Issue We Then Try & Find What Has Changed Since You Did Not Have Any Issues Before. Has Anything Changed Recently.

Added or Changed Something Electrical? Stereo Etc.

Any Kind of Repair Work??

Car Recently Was Exposed To a Lot of Water?? Water Intrusion at Cowl Can Cause Many Issues.

Car Was Made a Weekend Car Vs a Daily Driver?? Many With S-197's Simply Have To Use a Battery Tender If Car Is Not Used Much!

Bad Alternator.

Really a Lot of Different Causes and I Think We are At the Point Where We on The Site Simply Go To The Last Culprit on a Post So I'm Trying To Steer Towards a Back To Basics Approch This Time Around.

Take a Look At The STICKIES in This Section and There a Lot Are On Battery / Alternator.

As Far as Your Question on Chasing a Parasitic Loss Here is The FORD Guide.

https://themustangsource.com/forums/...ompany-549893/

Kc

 

Thanks for the response and moving to the proper section.
That's my frustration. Pretty much the answer to all your questions is "no".
The battery is less than 2 years old, and I have a battery tester. It passes crank and amperage tests.
No repair work has been done for a few years.
The audio system is original.
I put an aftermarket head unit in it about 6 years ago.
It's driven regularly, although not every day, since I work at home.
The alternator is only a few years old and works and charges great.

This just started out of the blue a month or two ago and the battery is suddenly drained to fully dead in a day or two.

I can't find any cause.

 

Ok So I Would Check Out The Parasitic Loss Pdf & Proceed. A Little Twist on The Alternator if I Recall is They Can Test Good and Still Have a Bad Diode & Cause a Loss. I Think a Thread Here I Will Post in a Sec Will have Some In Depth Alternator Info. I Would Just To Be Sure Check For P-Codes and Body Codes Even If You Don't Have a Check Engine Light To Narrow Down Search! If You Do Narrow Down To Alternator it is Imparative You get a Good Quality One & Might Also Look into The Denso Upgrade!

https://themustangsource.com/forums/...-phase-539499/

KC

 

Found This Info on Rock Auto.

Paragraph 6 Seems Interesting!

When the battery goes dead, the condition of the battery and the alternator are two of the first things to check. However, do not assume that if the battery is good then the alternator must be bad and the cause of the problem. My 1979 Chrysler 300 still has its original, never disassembled alternator. I have lost count of how many new batteries and electrical problems the car has had over the decades. Here are a few tips on how to use common tools to diagnose charging system problems to prevent unnecessarily replacing the alternator. These are general suggestions that may not apply to every car. Rely on your car’s repair manual (found under “Literature” in the catalog) for vehicle specific instructions.

1. Using a multi-meter, measure the voltage across the battery posts with the engine off. It should be 12 or 12.5 volts. If it is less than 12 volts, then the battery needs to be charged, something is draining the battery or the battery cannot hold a charge and needs to be replaced.
2. If the battery voltage is around 12 volts, then start the engine and again measure the voltage across the battery posts. It should have increased to 13 or 14 volts if the alternator is working and charging the battery. (Note: The computers on some newer vehicles will not raise alternator output to 13+ volts unless the headlights or some other system that draws a lot of electrical current is switched on first.)
3. If the battery voltage did not increase with the engine running, then verify the alternator and battery have good electrical connections. Make sure the battery cable terminals are tight and free from corrosion. Look for loose connectors or frayed cables. Use the multi-meter or a test light to verify the body of the alternator is grounded (zero resistance between the alternator and negative battery post).
4. If the battery voltage is well above 14 volts with the engine running, then the alternator could be producing too much current and overcharging the battery. Maybe the voltage regulator (internal to some modern alternators) is bad. Or the battery is weak and a vehicle computer has temporarily raised the voltage limit. It might still also be bad connections or loose wiring. Some vehicle lights being brighter than others can be a symptom of this type of problem, because the alternator produces more energy to overcome the resistance of a bad wire or connection.
5. The condition of the alternator belt is the next thing to check. Of course make sure the belt is not broken. Also look for a belt that is loose and slipping. It would probably be making noise.
6. If in step 2 the voltage across the battery terminals was 13 to 14 volts with the engine running, then the alternator is properly charging the battery. That is good news, but there is another alternator electrical problem to check for. I know from personal experience with a Ford 5.0L. that sometimes an alternator can charge fine when the engine is running but drain the battery when the engine is off. It probably has something to do with the rectifier diodes in the alternator not properly blocking current from draining away from the battery. This problem may be intermittent. It certainly was on my Ford 5.0. Disconnect all the electrical connections from the alternator when the car is put away for the night. If the battery never goes dead with the alternator disconnected but goes dead when the alternator is hooked up, then that might point to an alternator diode problem. RockAuto sells replacement diodes for some alternators. The diodes are buried so deep inside many modern alternators that replacing the entire alternator is often the most practical option.
7. If the battery goes dead when the car sits (engine off) with the alternator electrical connections disconnected, then something else is draining the battery. Check first for the most obvious battery drains such as any lights left on (headlights, trunk light, ashtray light, etc.). After that it gets harder to track down the problem especially on modern cars. Newer cars have systems that are designed to stay on for various amounts of time after the engine is switched off. In the next newsletter, I will offer some tips on tracking down specific circuits that are draining a battery.
8. Finally, there are the mechanical alternator problems. Unusual screeching or grinding sounds might come from a bad bearing in an alternator. However, the noise might also be coming from a loose belt, misaligned pulleys or worn out belt tensioner. Use an automotive stethoscope to verify where the noise is coming from. Avoid damaging new alternator bearings by making sure the belt pulleys are aligned, the belt tensioners are good, the belt is not over tightened, the alternator mounting bracket is not cracked or that there is not some other mechanical problem.

 

Thanks again for the info.
I will go over the components a bit more carefully.
Hopefully it's not the alternator as this is the one I have in it. It is quiet, smooth, and charges it up great at about 14.5v while driving (I have an in cab voltmeter).


https://www.americanmuscle.com/paper...or-0510gt.html

 

You Are Welcome!

If You Do Have an Alternator Issue There Are Still a Few Shops Out There That Can Rebuild Your Existing Unit. Just a Thought if That Happens! We Get So Used To Simply Exchanging Parts These Days Due To Time Issues Etc. We Don't Usually Think Around Those Lines!

KC

 

Hi, I did not read all of the above, so apologies if I am repetitive:

One common cause for this is the Shaker stereo system. One simple trouble-shooting method, is to pull the fuse for the radio/stereo system, and see if the draw goes away. Check the owners manual for the fuse number(s) and be aware there could be more than one.

Another way to test, is: disconnect the battery ground; and put an ammeter between the ground post on the battery, and a chassis ground. You should see the draw on the ammeter. Remove the fuses one by one, until the draw goes to zero. Now you have identified the circuit with the draw. Next you need to figure out what on that circuit is causing the draw; and in the meantime you can leave that fuse out, assuming it is nothing vital.