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Discussion Starter · #1 ·
I have a '67 Fairlane with a 351W and I've added an alternator with internal voltage control ,A/C, electric fuel pump and it's running a Duraspark ignition. All of a sudden the battery dies overnight. I've got full battery voltage with a meter between the battery positive terminal and the disconnected positive lead with everything off. The clock doesn't work. I've pulled the fuses one at a time and the voltage didn't change. I believe the only unfused hot wire goes to the ignition and I don't have any voltage at the coil with the ignition off. All lights, directionals, horn, etc. work fine. Not sure where to look next. Any advice?
 

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I have a '67 Fairlane with a 351W and I've added an alternator with internal voltage control ,A/C, electric fuel pump and it's running a Duraspark ignition. All of a sudden the battery dies overnight. I've got full battery voltage with a meter between the battery positive terminal and the disconnected positive lead with everything off. The clock doesn't work. I've pulled the fuses one at a time and the voltage didn't change. I believe the only unfused hot wire goes to the ignition and I don't have any voltage at the coil with the ignition off. All lights, directionals, horn, etc. work fine. Not sure where to look next. Any advice?
Hello Molon Labe,

Looking for a voltage increase on a high amp hour battery with low internal resistance whilst disconnecting loads is like looking for a needle in the haystack. Instead set your meter to 10 Amps current setting (or get a meter that has that function) and place the current meter in series with the battery. Most digital meters even in the 10 amp setting will still read out to the hundredths place in current which is more than enough to find a parasitic load left on. Once you have that in series now go back and pull fuses and start disconnecting items till the current reads near zero.

Assuming the battery is not at fault and is fully charged, to drain a battery overnight to the point where it will not crank you will have a 2-4 ampere constant draw on a typical 24 amp-hour flooded lead acid battery. It should be pretty obvious with that much load present somewhere in the car. Now if the battery is marginal at best to begin with, then something around an amp or less maybe enough to drain the battery to the point of non-cranking condition in 24 or so hours.

Also keep in mind that not everything from the factory uses the fuses in the fuse block. There are two circuit breakers inside the headlamp switch that feed all the safety items like headlamps, brakes lamps, horns etc. Also check if you have a deck lid lamp that is not going off when it is shut. Things like that.

Good Luck

Cheers
 

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I had an F150 that had a parasitic battery drain. Pulling the fuses didn't help. I ended up disconnecting the alternator and that was it. Something shorted inside and obviously no "alternator fuse" to pull.

Pat
 

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Discussion Starter · #4 · (Edited)
Hello Molon Labe,

Looking for a voltage increase on a high amp hour battery with low internal resistance whilst disconnecting loads is like looking for a needle in the haystack. Instead set your meter to 10 Amps current setting (or get a meter that has that function) and place the current meter in series with the battery. Most digital meters even in the 10 amp setting will still read out to the hundredths place in current which is more than enough to find a parasitic load left on. Once you have that in series now go back and pull fuses and start disconnecting items till the current reads near zero.

Assuming the battery is not at fault and is fully charged, to drain a battery overnight to the point where it will not crank you will have a 2-4 ampere constant draw on a typical 24 amp-hour flooded lead acid battery. It should be pretty obvious with that much load present somewhere in the car. Now if the battery is marginal at best to begin with, then something around an amp or less maybe enough to drain the battery to the point of non-cranking condition in 24 or so hours.

Also keep in mind that not everything from the factory uses the fuses in the fuse block. There are two circuit breakers inside the headlamp switch that feed all the safety items like headlamps, brakes lamps, horns etc. Also check if you have a deck lid lamp that is not going off when it is shut. Things like that.

Good Luck

Cheers
My meter won't read 10 amps. 2000 micro amps max.
Yellow Gadget Measuring instrument Technology Font

How about converting ohms?
 

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Sure, you could throw an inline resistor on your cable end to the battery terminal in order to measure current; I=V/R (Current = Volts / Resistance) across the resistor, but large wire-wound resistors to read up to 10A with a meter are costly for one use. The wait and cost may be outweighed by a cheap multi-meter that reads 10A at your favorite online store (random first find of something usable). It doesn't have to be highly accurate, and you could use that for more stuff, but it's your preference.

@1964Fastback - the alternator drain is an example of a blown internal diode or incorrectly wired dash light. If the free alternator test at you local parts store says it's good, it's your wiring.
 

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With the meter between the disconnected positive wire and the positive terminal it read 13.3 volts. After disconnecting the alternator it dropped to just over one volt.
Hello Molon Labe,

I think you found the problem. Of course just using a voltmeter doesn't tell you the amount of current, since most DVM's are about 10 megohms the fact it went to just over a volt easily tells you you are in the microamps at that point.

Just as PSIG stated, it's best to buy a meter with a usable 10 amp or more function. Heck even Harbor Freight was giving them away at one point. If you're going to keep an old car, it will be an invaluable tool for any other problems.

This internally alternator you bought, is it the "one wire" kind? If so they have a high parasitic draw by design and are pure crap in my opinion for a car that isn't a race car. Why not just put a Ford 1G 55 amp alternator and regulator back in the car?

Cheers
 

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Discussion Starter · #8 ·
Hello Molon Labe,

I think you found the problem. Of course just using a voltmeter doesn't tell you the amount of current, since most DVM's are about 10 megohms the fact it went to just over a volt easily tells you you are in the microamps at that point.

Just as PSIG stated, it's best to buy a meter with a usable 10 amp or more function. Heck even Harbor Freight was giving them away at one point. If you're going to keep an old car, it will be an invaluable tool for any other problems.

This internally alternator you bought, is it the "one wire" kind? If so they have a high parasitic draw by design and are pure crap in my opinion for a car that isn't a race car. Why not just put a Ford 1G 55 amp alternator and regulator back in the car?

Cheers
I've ordered a meter with the 10 amp feature that will be here tomorrow. I'm using the Ford 3G alternator because it mounts to the stock Ford 150 serpentine belt frame. I've also added AC so I don't think 55 amps will git er done.
 

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This internally alternator you bought, is it the "one wire" kind?
Yeah, I'll agree with this one, but for more reasons such as reduced voltage control due to omitting the sense wire, and a dead warning light. The alternator regulator is reading the alternator output, not the battery or system condition. Most of the conversion regulators don't begin charging until about 2500 rpm. Little side-effects of each, such as that also makes a dead-battery push-start a bit of an issue if I ever need that. While many are happy with their 1-wires, you should be aware of the compromises.

[EDIT] For clarity, some regulators don't activate until 2500 rpm initially, but once working, will work down to low rpm. This just means that some need to be revved to start charging, and after that it's fine.

One-wire alternators are attractive for simplicity, but you have to ask yourself—if it works so well, why did all those cars use the two extra wires? ;) For me, the compromises aren't worth avoiding the connection of 1 or 2 wires. Do your thing.

Trivia: did you know you can do limited diagnostics with your alternator "idiot" light? Such as whether it gets dimmer or brighter at higher rev's, what that means, and more.
 

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I've ordered a meter with the 10 amp feature that will be here tomorrow. I'm using the Ford 3G alternator because it mounts to the stock Ford 150 serpentine belt frame. I've also added AC so I don't think 55 amps will git er done.
Howdy Molon Labe,

Factory air con cars came with a 55 amp alternator in the mid 60's. I still have the Ford 1G 55 amp alternator in my '68 XL with working factory air and even have upgraded 200/560 (low/high) watt headlamps. No problems.

Do you have the 3G alternator wired correctly? Is the alternator indicator lamp wire connected to the alternator lamp in the dash?

Cheers
 

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Discussion Starter · #11 ·
Howdy Molon Labe,

Factory air con cars came with a 55 amp alternator in the mid 60's. I still have the Ford 1G 55 amp alternator in my '68 XL with working factory air and even have upgraded 200/560 (low/high) watt headlamps. No problems.

Do you have the 3G alternator wired correctly? Is the alternator indicator lamp wire connected to the alternator lamp in the dash?

Cheers
Alternator lamp is wired in and working. Alternator is putting out 14.6 volts at idle - about 900 rpms. I've got a voltmeter in the car and it's always charging while driving.
 

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Being an older car, do you still have the older radio? Some had to be turned off when the car wasn't running, (some). That or pull all the fuses and check the next day. With the key off check for voltage where it shouldn't be. At the coil and other places.
Hate solving electrical gremlins.
 

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Discussion Starter · #13 ·
Being an older car, do you still have the older radio? Some had to be turned off when the car wasn't running, (some). That or pull all the fuses and check the next day. With the key off check for voltage where it shouldn't be. At the coil and other places.
Hate solving electrical gremlins.
Radio is not hooked up. Pulled the fuses one at a time and voltage didn't drop. No voltage at the coil.
 

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With the meter between the disconnected positive wire and the positive terminal it read 13.3 volts. After disconnecting the alternator it dropped to just over one volt.
Could you Please Define your Connection and Disconnection? Please do not use any Meter in Ohm Position when you have the Battery connected Since you don't have the expertise using a DVM. You can use your any DVM to perform testing for a Close 12V Draw but as mention it may be a Needle in a Haystack. But if you have already removed all the Fuses it will take less time. I am confuse on your statement on the exact Process and Wire you perform. The 1967-68 Mustang wiring diagram is almost the same as the 67 Fairlane. Please see attached 1967-68 Mustang Wiring Diagram.

Ricky, Nice to see you again.

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