Large Parasitic Draw

whisperer

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Dec 25, 2000
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Heya, My 2005 V6 auto oem standard stereo car has developed a large battery draw. With a test light across the removed neg batt cable I have removed all the fuses and relays in both boxes one by one and have not lost the draw with any of them. The last post on here that I could find about this problem was inconclusive and ended in 2014.

Anyone have an idea on this? Has there been any concrete reason that has been found for this issue? TIA.
 
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7991LXnSHO

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If you see at the parts counter, one of the things I would offer to test is the alternator. Sometimes, a diode can go out.
If pulling the fuses did not work, I’d look for the circuits with fusible links.
I hope they have a wiring diagram for you in this section.
 

whisperer

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Thanks for the reply. I already pulled the alt connections, big and little and no change. Now I have other weird electrical issues happening after disconnecting the battery...... There is a reason I like vintage cars...... :(
 

7991LXnSHO

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A modern car that works right is a joy. One with electrical gremlins can drive you nuts. Too many wires and modules!
I know Dodge has hook ups to diagnose the whole electrical system remotely when the local mechanic is stumped. (And yes, Chrysler/Jeeps sometimes need this tech.) Before you decide to start a bonfire or the car does, you might ask Ford on a Mustang this recent. There may even be a TSB.
 

whisperer

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Sorry about the late reply, I was on vacation. Instead of disappearing like many when the problem is solved let me leave this info so the next person doesn't have to chase their tail as much as I did. This will be long and detailed so have patience. If your car keeps killing batteries and alternators, and won't start after it sits for a while THIS is highly likely your real issue. Of course your results may vary.

My car did not have a draw, it APPEARED to have a draw. It tested as a large draw after charging the battery and I did this multiple times trying to locate the draw.

The battery was bad, making it effectively a 10 volt battery because it had a bad cell. My charger would try to get it to 12+ volts and would be totally successful, only to have it drain back to 9.5-10 volts over the next few hours. Yes, my test light lit between the neg batt term and the cable, however with test light removed if the cable was totally disconnected the batt would still drain down. OK fine, new battery.

BUT WAIT, THERE'S MORE....

My battery had been damaged by radical overcharging. This is where you need to pay attention..

On these cars and later the PCM controls the regulator inside the alternator. With a brand new fully charged battery my alt was still charging max, as if the batt was dead. After a long roundabout troubleshooting effort I found that the ground cable from the engine to the body was bad, and even new it is too small. My PCM was reading low voltage and cranking the alternator to full blast, trying to kill the new battery.

This explains why some cars regularly go through batteries (overcharged daily) and alternators (constantly charging at max capacity). Also why the car won't start after sitting (battery has a dead cell from being overcharged).

THE FIX.

If you pull a batt cable, charge the batt and then let it sit for several hours and it drops to 10 volts -- you will first need a new battery.

THEN add a full sized batt cable sized ground cable from one of the alternator mounting bolts to the bolt that the batt ground cable bolts to on the shock tower. I used a 18" black ground cable with 2 ring ends, available at most auto parts stores.

NOW your system is actually fixed.

Mine immediately started acting correctly, charging correctly, had 12.8 volts at the PCM. Starts every time even after sitting for a few weeks....

Hope this helps somebody.
 

7991LXnSHO

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Thanks for the summary, and glad you are back on the road. Upsizing that ground cable is supposed to be part of the alternator upgrade process. I wonder how many people miss and risk a fire, overloading the other grounds or ruining clutch or shift cables that try to run current.
Even if the charging system is stock, a bigger ground cable is not going to hurt.
 

whisperer

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Dec 25, 2000
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Yeah, so sort of yes and sort of no. I have done no alternator upgrade. I think what you are referring to is the 3/4G alternator burning plug problem? Those replacement alts come with a new connector as the OEM melts. That is not the problem here.

The 2005+ V6 cars have a smallish stock ground wire from the rear of the left bank cylinder head that bolts to the pinch weld above it on the firewall. It is sorely undersized and then corrodes on top of that. All of the starter amperage and alternator amperage, plus, gee whiz, the coils, sensors, TB motor etc. have to try to ground through this "barely adequate when new" ground strap.

I have been told that the GT's have a separate additional ground strap from the right side engine mount engine-side bolt to a bolt on the body. I don't have one in the shop. Maybe someone can confirm or deny? I know the V6's are missing this extra strap.
 

74stang2togo

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Sorry about the late reply, I was on vacation. Instead of disappearing like many when the problem is solved let me leave this info so the next person doesn't have to chase their tail as much as I did. This will be long and detailed so have patience. If your car keeps killing batteries and alternators, and won't start after it sits for a while THIS is highly likely your real issue. Of course your results may vary.

My car did not have a draw, it APPEARED to have a draw. It tested as a large draw after charging the battery and I did this multiple times trying to locate the draw.

The battery was bad, making it effectively a 10 volt battery because it had a bad cell. My charger would try to get it to 12+ volts and would be totally successful, only to have it drain back to 9.5-10 volts over the next few hours. Yes, my test light lit between the neg batt term and the cable, however with test light removed if the cable was totally disconnected the batt would still drain down. OK fine, new battery.

BUT WAIT, THERE'S MORE....

My battery had been damaged by radical overcharging. This is where you need to pay attention..

On these cars and later the PCM controls the regulator inside the alternator. With a brand new fully charged battery my alt was still charging max, as if the batt was dead. After a long roundabout troubleshooting effort I found that the ground cable from the engine to the body was bad, and even new it is too small. My PCM was reading low voltage and cranking the alternator to full blast, trying to kill the new battery.

This explains why some cars regularly go through batteries (overcharged daily) and alternators (constantly charging at max capacity). Also why the car won't start after sitting (battery has a dead cell from being overcharged).

THE FIX.

If you pull a batt cable, charge the batt and then let it sit for several hours and it drops to 10 volts -- you will first need a new battery.

THEN add a full sized batt cable sized ground cable from one of the alternator mounting bolts to the bolt that the batt ground cable bolts to on the shock tower. I used a 18" black ground cable with 2 ring ends, available at most auto parts stores.

NOW your system is actually fixed.

Mine immediately started acting correctly, charging correctly, had 12.8 volts at the PCM. Starts every time even after sitting for a few weeks....

Hope this helps somebody.
You could also just take the battery to a parts store to be load tested. This will confirm that the battery only had a "surface charge" when pulled off the charger and actually can't maintain the correct level of charge anymore.
 

whisperer

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Dec 25, 2000
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I could except I have a battery load tester. Unhooking a cable and leaving it on a VOM for a few hours will tell you the same thing, but more reliably. Why does it say I'm a New Member when I've been on Stangnet for 20 years?
 

74stang2togo

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I could except I have a battery load tester. Unhooking a cable and leaving it on a VOM for a few hours will tell you the same thing, but more reliably. Why does it say I'm a New Member when I've been on Stangnet for 20 years?
Because you've posted all of 13 messages.
 

74stang2togo

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I don't say something unless it's worth saying. Can't stand people that just say sh!t just to hear themselves talk.
That's your prerogative. It's also why you haven't ever passed the threshold to move up from "new member". :nice:
 

7991LXnSHO

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No, I am referring to the ground cable, not the melting plug problem. I was thinking how your problems and fix are also common in Fox, sn95, or any vehicle that gets a mega stereo or light system alternator upgrade. A barely adequate when new. ground (negative) wire will not be be up to the flow of the positive wires and the alternator output, just like you describe. A "barely adequate when new" ground strap can get hot, create a resistance, and the electricity will try to flow back through any extra ground paths it can find. B&M auto shift cables do not last long when there is a weak or missing ground strap. The kid blames the shifter company, and when the countryman and manager convince him to install a new ground cable, the kid usually realizes it was left off when he had the motor and transmission out. That's not as common in your newer Mustang, but it will be as they age.

It is strange the GT's would have an extra strap or ccable, rather than making sure both were up to electrical demand. It's hardly the first time Ford or other maker skimped on wire size in some circuit for a little cost and weight savings.
I'm glad you found the issue before it burned up something or caused a catastrophic battery failure.

Yeah, so sort of yes and sort of no. I have done no alternator upgrade. I think what you are referring to is the 3/4G alternator burning plug problem? Those replacement alts come with a new connector as the OEM melts. That is not the problem here.

The 2005+ V6 cars have a smallish stock ground wire from the rear of the left bank cylinder head that bolts to the pinch weld above it on the firewall. It is sorely undersized and then corrodes on top of that. All of the starter amperage and alternator amperage, plus, gee whiz, the coils, sensors, TB motor etc. have to try to ground through this "barely adequate when new" ground strap.

I have been told that the GT's have a separate additional ground strap from the right side engine mount engine-side bolt to a bolt on the body. I don't have one in the shop. Maybe someone can confirm or deny? I know the V6's are missing this extra strap.
[
 

kiddiccarus

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I guess I will be installing a Ground Cable soon to that shock tower. I don't have the stereo in this but I have the draw. I basically keep the positive cable unhooked (cutoff installed) when I am not driving for now
 
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DaBard

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Jun 17, 2020
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Whisperer, thank you for the hard work and very clear exposition of the problem and solution.
Older vehicles do indeed suffer from ground fault issues, mostly due to old age of the connectors and, in northern states,
the "salt tax" that takes its toll, even if the vehicle isn't driven in winter.
 

7991LXnSHO

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I don't say something unless it's worth saying. Can't stand people that just say sh!t just to hear themselves talk.
And there are so many other creative and expressive words to use (if not in extreme distress) that you might as well use interesting ones when you do attempt to communicate.
 
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