Dead short?

[70b5bluerunner]

My brother had some restoration work done to his 70 hemi charger. He now has a major electrical issue that no one can find. When you pull all the fuses there is still a strong draw on the battery, pulling it dead overnight. The alternator was rebuilt by a professional service. The engine and trans were pulled to paint the engine compartment and underneath. The car was taken apart for paint but the dash was not removed. I know it's not much to go on but looking for a place to start. Thanks for your time.

 

[pnora]

Pretty simple system for a competent mechanic to diagnose. It is a draw not a dead short. With all the fuses pulled that does not leave much else. Did you feel the alternator? It should be warm. You could try unplugging it. With a meter you should be able to find it a few minutes. How many amps is the draw?

 

[65CopCar]

Disconnect the alternator and see what happens.

 

[RJRENTON]

My brother had some restoration work done to his 70 hemi charger. He now has a major electrical issue that no one can find. When you pull all the fuses there is still a strong draw on the battery, pulling it dead overnight. The alternator was rebuilt by a professional service. The engine and trans were pulled to paint the engine compartment and underneath. The car was taken apart for paint but the dash was not removed. I know it's not much to go on but looking for a place to start. Thanks for your time.

IMO....parasitic losses, such as those you mentioned, usually due to low resistance to ground. Like the dome light, glove box light, cigar lighter, AND the alternator, even though: "The alternator was rebuilt by a professional service.". What did they "rebuild" in the alternator? Diodes are susceptible to damage causing a low resistance to ground. As noted previously, how much current is being lost? Disconnect the alternator output wire and check for current flow....zero is the only acceptable value. Just my opinion of course....
BOB RENTON

 

[zyzzyx]

Take the alternator to Auto Zone and have them test it. Check the battery overnight for voltage
while being disconnected from the car. The battery might be bad. Put a 12v light bulb between
one of the battery leads and see if it lights. if it does, there still is a draw. Good luck!

 

[twecomm]

Alternatively, you could use a digital volt meter and measure just the battery, totally disconnected. While battery is disconnected, you would still want to have the fuses pulled. While you have the battery disconnected, remove the large lug from the alternator and temporarily insulate the lug making sure it can't short to ground, Re-connect battery and measure. With alternator disconnected, battery volts reading should be same measuring battery only. If you see a voltage drop of any amount with alt connected, you got an alternator problem, likely a defective diode or some other resistive wiring condition causing the voltage drop or a bad battery that just won't hold a charge.
Always best to have the battery disconnected when doing anything with the cars electrical system.

 

[dan juhasz]

disconnect alternator first, after that amp meter

 

[dan juhasz]

oh, if you have a chinese voltage regulator unplug it also, they are trash

 

[twecomm]

One thing at a time...

 

[Geoff 2]

I had a 'mini' 50 amp alt that had an internal 'leak' to ground that would rain the battery in a few days.

 

[RJRENTON]

Take the alternator to Auto Zone and have them test it. Check the battery overnight for voltage
while being disconnected from the car. The battery might be bad. Put a 12v light bulb between
one of the battery leads and see if it lights. if it does, there still is a draw. Good luck!

WHAT TESTS ARE BEING PERFORMED?? Do they test for max output? Individual phases to ground? Positive diodes to ground ; negative diodes to ground. Do they perform a hi-pot test for overall stator windings resistance to ground? You have to be specific about the tests......I'm betting they just do minimal tests as some tests I described require dissembling of the alternator. Most auto parts stores/techs have no real knowledge of how the alternator operates. IMO....you're wasting your time at the auto parts store........
BOB RENTON

 

[zyzzyx]

Well, Hell No they don't do all of that! WTF? Just a basic test that let's you know if it's any
good or not. You have to start somewhere. Next time I'm there, I'll ask the Kid who makes
$10../Hour your questions! I'm taking a screen shot of it now!

 

[RJRENTON]

Well, Hell No they don't do all of that! WTF? Just a basic test that let's you know if it's any
good or not. You have to start somewhere. Next time I'm there, I'll ask the Kid who makes
$10../Hour your questions! I'm taking a screen shot of it now!

Ok.....but WHAT TESTS do they do? Describe what a "basic" test encompasses. The $10/hr counter person had no business passing judgement on my equipment without any prior knowledge of my equipment and how it functions. And, what is sad, is the person that asks for the "test" or evaluation has no clue either as to what may be faulty, and is relying on a person that knows LESS than he, and then accepts the results, without question. Result: the auto parts store makes $$, the counter person makes $$, the consumer pays the price ....possibly for a part that does not fix the problem. I would be curious as to the results of your inquiry.......
BOB RENTON

 

[70b5bluerunner]

Found the problem. It is in the clock somehow. Still trying to sort it out.