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Re: Battery drain (2/12)
 7/22/17 7:53pm
F4Gary
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 968

Bad battery
Bad alternator

That's where I would start.  Get it.....start?


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Re: Battery drain (3/12)
 7/22/17 8:52pm
stingrayjim jrLifetime Member
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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed


Joined: 7/5/2002
Posts: 3942

Definately check the alternator,  get a voltmeter(don't solely rely on the dash meter) and check the voltage at the battery before starting(if well charged it will read around 12.6 volts) and then start engine, and recheck the voltage at the battery again, it should be higher than the previous reading, somewhere in the 13 volt range, maybe just at 14.... if not, idle up the engine around 1000-1200 and check the voltage, if still nothing then its probably the alternator....    typically the alternator will keep the engine running regardless of the battery, but not all alternators will work without a battery energizing the alternator, most 'older' alternators will, newer ones not so much...)  

Now, if your battery is reading under 12.5 volts, charge it.... and if you can hook up a voltmeter to it while trying to start the engine,  and read the voltage while it is turning over, and it falls down to 10.5 volts or lower, then your battery is failing..   (may as well check the water in the battery while you are fooling with it, if ONE cell is dry or extremely lower than the rest, you may have a bad cell)  

only other thing i can think of off hand is you might have a bad battery cable, but you would notice your gauges getting weird too....  needles bouncing around and such....    

almost forgot,  if the diode in the alternator is gone, it will output voltage, however, when the engine is off, the alternator will drain the battery also, with a bad diode.... 

but to me, just by what you describe, it does sound more like the alternator, and the car is running off the battery,  once the voltage gets so low on the battery, there is not enough there to keep the ignition going, or, if you turns the lights on, it kills the motor(even brake lights)... 




|UPDATED|7/22/2017 5:52:25 PM (AZT)|/UPDATED|


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StingrayJim
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Re: Battery drain (4/12)
 7/22/17 9:23pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 588

Most auto parts stores will test both your alternator and your battery for free.

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1973 L-82 4 spd

Re: Battery drain (5/12)
 7/22/17 10:39pm
rep69
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Chesapeake, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 130

Thanks for the info. The alternator was checked and it is putting out the correct voltage. The alternator was just overhauled a couple of months ago.Battery is a red top optima and it is new.  Now on to checking the cables.
Re: Battery drain (6/12)
 7/23/17 3:19am
stingrayjim jrLifetime Member
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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed


Joined: 7/5/2002
Posts: 3942

well, i would still test the alternator, just for peace of mind... even just being rebuilt, 'things' happen....   and being an Optima battery, they do fail too...especially since Johnson Control bought out Optima and quality kinda suffered...  

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StingrayJim
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Re: Battery drain (7/12)
 7/23/17 10:55am
F4Gary
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 968

Optimas are definitely not what they used to be.

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Re: Battery drain (8/12)
 7/23/17 11:04am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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Has the voltage been checked AT the battery while running? Doesn't matter how the alternator works off the car if it doesn't get the voltage back to the battery. Assuming your '69 still has the separate voltage regulator on it, I would start with that. A bad/loose connection anywhere in the system will fail more when hot than cold. Dying while driving points to a loss of voltage due to no alternator input....whether it's because of a loose connection, or failing alternator output, or faulty voltage regulator. Other thing could also cause it to die like that, but your particular combination of no start when hot, having to jump it off, and it dying while driving points to a loss of voltage issue.
Put a voltmeter on the battery and see if the voltage takes a dive while driving. If it does, check the voltage at the alternator at the same time.
Check all of the battery cable connections on BOTH ends. Battery ground is under the driver seat, connected to the frame. The engine ground cable comes from the passenger side frame over to the engine block, usually right around the starter/engine mount.
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Re: Battery drain (9/12)
 7/23/17 3:06pm
rep69
Former Member

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Chesapeake, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 130

Thanks. I had the alternator checked while on the car and running. It is producing the correct volts. The battery is new and it was checked at local auto store.  The starter is a new mini type. factory manifolds .  I can check the cables and grounds.
Re: Battery drain (10/12)
 7/23/17 8:06pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 588

Another way to rule out the alternator is to disconnect the battery with the car running. If the car dies then it's the alternator because once a car has been started and is running, the alternator should carry it without the battery.  

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1973 L-82 4 spd

Re: Battery drain (11/12)
 7/23/17 9:41pm
rep69
Former Member

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Chesapeake, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 130

Thank you for the info.
Re: Battery drain (12/12)
 7/30/19 6:21pm
rlu1968
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427


Joined: 11/28/2003
Posts: 228

If all else fails check your wipers and make sure they are parked. I had this problem for years and went through several alternators and even replaced a new battery. The 68 at least has to have full rotation of the wiper arms. If someone had hit the switch with the wiper door closed It would allow the wipers to activate power and not be able to park themselves. 

Open the wiper door (override switch) and switch on the windshield wiper switch and then turn them off and make sure they park to get the power drain off. 



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