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Discussion Starter · #1 ·
All of a sudden my 66 is draining the battery overnight. Down to 3-4 volts. The only change I’ve made recently is that I reinstalled the aftermarket fuel gauge, with lights. So I lifted the wires from the gauge, slowly recharged the battery over two days, reconnected the batt and it was dead the next morning
I put my meter between the pos batt cable and the pos post and on the milliamp scale I’m showing a intermittent 00.01 mA. To me that is nothing.
When fully charged, I tested the battery and it says it’s good, no bad cells, minimum resistance.
Could a bad ignition switch cause a drain? I suspect my ignition switch in an intermittent non-starting issue so I’ve got a new switch coming.
 

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Charge the battery up and then leave it disconnected and at first if you measure the voltage it may be high due to a surface charge but come back to it later and take a measurement and it should stabilize at around 12.5V or so but if after a day or two with nothing connected to it, if the voltage keeps dropping to like 11V, then a day later to 10V, then the battery is shot.

I did have a weird one years ago with a mercury switched trunk light and when parked on a flat surface the trunk light was off but then when parked on an incline the light would be on unknowingly and then if the car sat there a few days in that position, the battery was too low to start the car.

Jim
 

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Discussion Starter · #4 ·
I let it sit disconnected overnight and yesterday morning it was 12.4v.
I’m heading to my shop shortly to check it again.
 

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So it is a drain... new dome light fixture.. they are said to be a drain due to chrome plating where the bulb attaches. so a Short.
Pin switches in the doors? Trunk light? under hood light? glove box light? Thinking easy to check things first then going to maybe Ignition switch.
Drain due to a short where wiring harness may have chaffed on body? That should take out a fuse and shown as blown but...?
Corrosion on starter Batt cable connection?
 
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I let it sit disconnected overnight and yesterday morning it was 12.4v.
I’m heading to my shop shortly to check it again.
Just checked. So after another 24 hours of being disconnected the battery is at 12.04v.
So with the battery not connected to anything (disconnected) you lost 0.32V with it just sitting there all by it's lonesome.

I'm thinking battery issue.

If you have the time, see what happens in another day. If with it still disconnected and it goes down to let's say 11.72V (another 0.32V drop), then I will say a battery issue.

I don't know if it's an old wives tale but maybe wipe off the top of the battery as I have heard sometimes junk or a film on the battery can connect one post to the other and create a drain.

Jim
 

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Discussion Starter · #11 · (Edited)
I’m not in too big a hurry since a project parked behind it morfed into more than I thought so it’s kinda trapped.
The battery is clean and less than a year old.
I’ll check it again tomorrow AM.
 

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I disconnect the battery after I use my 1966, it also has a slow drain on about the 0.01 mA range. Most likely the 50 year old insulation on the wiring. It’s fine for the day, stopping here and there but leave it for 2 weeks to a month. The battery will be dead, most lead acid batteries will be damaged the first time this happens. It will probably still charge up but will have less capacity and the next time you need it may not be there. Easier to disconnect, it also will slow do a thief, probably not long but some.
 

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I did notice in this pdf that they are testing on the neg battery post/cable. I’ve been using the pos post/cable to see if there was any amperage.
Does it make a difference? Why?
Current flow is current flow.

A draw is detectable whether you break the positive or negative connection. The only thing that will change is the flow detected by the meter (polarity). A digital meter may show the (-) negative sign in front of the digits. An analog meter (like in my avatar) will peg the wrong way and could damage the meter needle movement.
 

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I did notice in this pdf that they are testing on the neg battery post/cable. I’ve been using the pos post/cable to see if there was any amperage.
Does it make a difference? Why?
If you do a test on the positive side or the negative side, the amperage will be the same.

What is of concern is safety with making a connection wrong or a connection while doing the test touching ground from a power side.

Others can explain it more in depth or provide links to previous discussions on this but like anything else, take you time, make sure things cannot become shorted or a connection made that you did not want to happen.

When I was doing some tests on my 68 I put a towel down, made sure the test wires and connections were in good spots and then took measurements.



I then at another point did my amp draw test between the positive post and the positive cable end. I did it with no issues but not the safest BUT I took my time and was careful.



Jim
 

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Discussion Starter · #17 · (Edited)
11.99 volts this AM after being disconnected for another 24 hours. Battery tester now says recharge before testing.
Off to the battery store I guess…
Back to the original question because this whole mess started somewhere, can a bad ignition switch drain a battery down to 3-4 volts in a day or two?
 

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11.99 volts this AM after being disconnected for another 24 hours. Battery tester now says recharge before testing.
Off to the battery store I guess…
Back to the original question because this whole mess started somewhere, can a bad ignition switch drain a battery down to 3/4 volts in a day or two?
You said in your earlier posts that the meter read .01MA. I'd say the answer to your question is no in your case. A battery discharging on it's own (not connected to anything) means it's bad.
 
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I don't see how the ignition switch at the bottom of the steering column could do that unless it was heavily damaged or corroded.

Rick

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11.99 volts this AM after being disconnected for another 24 hours. Battery tester now says recharge before testing.
Off to the battery store I guess…
Back to the original question because this whole mess started somewhere, can a bad ignition switch drain a battery down to 3-4 volts in a day or two?
I would get a new battery, check it for proper charge as it might not be 100%, and if needed throw it on a charger for a bit, do an amp draw test before finalizing connections and then after a bit if it was on a charger take a volt measurement and then come back tomorrow and take another volt measurement.

The whole mess might have just started with the battery saying it's had enough and it was just time to be replaced.

You stated originally an intermittent 00.01A draw and to me this to is minimal. Not 00.00A which is nothing but maybe you have an aftermarket radio that draws a very small amount of current to retain the presets or clock section on it.

If you are worried about the new battery draining, get into a daily routine to check levels.

You could have an intermittent draw and if you take it out somewhere and then come back to it a day later after that and the battery level is lower or going down, then you have some work to track this down but cross that bridge when you need to.

Jim
 
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