1963 Corvette battery drain

[Patrick H.]

Almost done with the 63. I think this is the last issue (?).

I've had it twice in the last couple of weeks that the battery is dead when the car sits for a week.
Lights off, doors closed, and theoretically the only thing running is the clock.

Yesterday I checked the battery, which is at 12+V when charged overnight. And, if I have the battery disconnect open it can sit for days and works fine.
I opened the blade-type disconnect, checked the current between the two sides, and there is a 0.09 mA drain when the car is sitting. If I remove all of the fuses, the drain is the same. If I remove the gray 2-prong connector from the back of the alternator, the drain goes down to 0.035 mA.

Having said that, 0.09 mA and 0.035 mA seem like very small draws, but would they drain a relatively new battery in a week?
Is the change in draw enough to suspect the alternator? It's a rebuilt one, but as usual no guarantee as to the quality of the build.

Electrical issues are my weak point, so all suggestions welcome.

PH

[Harry S.]

Re: 1963 Corvette battery drain

Shot in the dark.

Take out the glove box bulb and check the drain. If the drain goes away, adjust the glove box switch to a different position. Also do the same with the courtesy lights if a convertible. If it's a coupe you can see the roof light if the door switch is adjusted incorrectly.

[Duke W.]

Re: 1963 Corvette battery drain

.09 mA is .00009 amp. Do you mean .09A, which is 90 mA (milliamp). That's high for a vintage car. There is a slight leakage through the alternator., but should be no more than about 10-20mA. If you remove both the connector and the output wire connected to the stud the drain should go to zero. The normal drain should not kill the battery in a week, but it's a good reason to have a battery isolation switch for cars that are not driven daily or near so.

Modern cars draw around 50 mA due due to refreshing all the memories.

Do Harry's recommended test, too, and be sure the alternator is grounded.

Duke

[Richard M.]

Re: 1963 Corvette battery drain

Yes. 0.09mA is negligible. Might want to double check that reading again.

Harry's idea is a good one. Put your cell phone in video mode and lay it in the glove box, close the door, wait a few seconds, then view the video for on/off proof.

Also, Which voltage regulator is installed, stock or solid state electronic? I once had a SS VR that was bad on our 63. Kept draining the battery. I leaned on the warm alternator one morning and it was warm. VR was bad, energizing the field.

A stuck contact on a stock points VR can also be a problem.

Rich

[Patrick H.]

Re: 1963 Corvette battery drain

My meter showed 0.09, and the label in the corner said mA. So, that's what I reported. I can try and get a picture if you wish.
I, too, was thinking it was negligible but yet it's having issues.

The reading with the gray 2-wire connector disconnected with or without the other two wires (main red, black ground) connected to the alternator was the same - 0.035. Disconnecting the alternator gray plug made the biggest change, but 0.035 drain remained. I assumed that could be the clock.

It's a stock voltage regulator.

The glove compartment light did come to mind. I can make my barn quite dark, and don't see any courtesy lights on but will check the glove box via video.

[Stephen L.]

Re: 1963 Corvette battery drain

Just remove the glove box light bulb and see if that affects your current reading..........

[Mark E.]

Re: 1963 Corvette battery drain

Wondering advice so far. I would also remove the cigar lighter as a check.

[Edward J.]

Re: 1963 Corvette battery drain

Pat, being around cars my whole life most battery drains lead to some on (ie lights, relays staying on)causing the drain, these old cars do not have a lot options so it’s very limited. My question is are wire harnesses original? Sometimes a constant power wires can rub through wire insulation and contact another wire that is being powered from the constant 12 volt circut. I have seen a situation like yours where I install a new AC Delco battery it would go dead, this through me for a loop, the way I found that the battery was is bad was to unhook battery after fully charging the battery 12.66 volts.and measure the voltage before I left for the night and then in AM measure it again, voltage should be the same. Remember the surface charge on the battery after charging, just turn headlights,on for 15to20 seconds to remove surface charge. If someone has added a aftermarket radio be sure to make sure they have it wired correctly (12volt and ignition on 12volt)