Battery drain
Thread Starter
Advanced
Joined: Jul 2021
Posts: 70
Likes: 31
From: San Clemente, CA
Battery drain
My '69 L46 has about a 1.5 amp drain, which kills the battery overnight. Being a normal size human there's no way I can get to the fuses to check circuits, but there are no random lights on and nothing running except the quartz clock. I've been disconnecting the battery whenever it's parked for a while and will continue to do so if only for safety concerns, but I'd still like to solve the problem. A friend suggested that it could be because of a bad diode in the alternator.
Does that sound reasonable? Any way to check it while it's still in the car? Any advice would be appreciated!
Does that sound reasonable? Any way to check it while it's still in the car? Any advice would be appreciated!
Instructor
Joined: Jan 2025
Posts: 132
Likes: 78
From: Mass/Rhode Island line
I am considering installing a battery disconnect switch in my 72 Corvette. I know it won't help with your draining issue,but it might prevent the battery getting drained on a daily basis. Mine doesn't have a battery drain issue,but I don't leave any cars in my garage with the battery connected.
Melting Slicks
Joined: Oct 2003
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From: Chapel Hill NC
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Cut off switch will hide your problem but save the battery. Diode in alternator may be culprit. Drivers seat comes out fairly easily and will give more access to fuse panel
Last edited by pltmgr; Mar 8, 2025 at 05:43 PM.
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From: Sunshine Coast, Queensland, Australia
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Bad diode in the alternator is a common issue. Just disconnect the wires from the alternator, one plug and one nut. Then test again for a drain. Shouldn't take 5 minutes.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
If the quartz clock is still running, it isn't the clock. If the clock is NOT operating, it could be the problem. But, bad diode in the alternator 3-pack is quite possible. Also possible is a ground leak path in one of the door AJAR switches. 1.5 amp leak is a pretty big dump. How did you go about measuring that
Melting Slicks
Joined: Feb 2018
Posts: 2,329
Likes: 725
From: Marietta GA
Does your car have the light in the cubby / glove box behind the seats? On my 73, I noticed it was on even though the rug covered door was closed, by chance I went into the garage and my motion activated lights didn’t turn on. Simply check your car at night with out opening the door and look for a light around the top of the door. I changed all the interior bulbs to LEDs so my battery never died, even if the light stayed on.
Burning Brakes
Joined: Sep 2016
Posts: 960
Likes: 449
From: Dutchess county New York
I have the same car and you need to get to the fuse box and start pulling fuses. If the car is elevated a little on ramps or cribs that does make it easier, throw a packing blanket over the sill.
I actually replied because of what @72 Steel Cities 454 said: a battery disconnect on these old cars is more than just a good idea. My house is worth a lot more than my 'vette plus I sleep in it.......
I actually replied because of what @72 Steel Cities 454 said: a battery disconnect on these old cars is more than just a good idea. My house is worth a lot more than my 'vette plus I sleep in it.......
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Thread Starter
Advanced
Joined: Jul 2021
Posts: 70
Likes: 31
From: San Clemente, CA
If the quartz clock is still running, it isn't the clock. If the clock is NOT operating, it could be the problem. But, bad diode in the alternator 3-pack is quite possible. Also possible is a ground leak path in one of the door AJAR switches. 1.5 amp leak is a pretty big dump. How did you go about measuring that
Thread Starter
Advanced
Joined: Jul 2021
Posts: 70
Likes: 31
From: San Clemente, CA
I am considering installing a battery disconnect switch in my 72 Corvette. I know it won't help with your draining issue,but it might prevent the battery getting drained on a daily basis. Mine doesn't have a battery drain issue,but I don't leave any cars in my garage with the battery connected.
Thread Starter
Advanced
Joined: Jul 2021
Posts: 70
Likes: 31
From: San Clemente, CA
Does your car have the light in the cubby / glove box behind the seats? On my 73, I noticed it was on even though the rug covered door was closed, by chance I went into the garage and my motion activated lights didn’t turn on. Simply check your car at night with out opening the door and look for a light around the top of the door. I changed all the interior bulbs to LEDs so my battery never died, even if the light stayed on.
Melting Slicks
Joined: Sep 2006
Posts: 2,821
Likes: 470
From: Wichita Kansas
