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Help with a long-standing SLOW electrical drain

gt289

gt289

Active Member
Car is a '68 coupe I've had since new. Problem is fairly recent- no more than 5-6 years.
I've got the battery on a master switch, otherwise it would be dead in a week or so.
Out of boredom, I decided to delve into the problem yesterday.
Alternator rebuilt (not reman) a few years ago and there's an electronic voltage regulator.
Putting a test light in series between the battery's positive terminal and the cable doesn't
illuminate the light. If you open a door it does, but it's dim.
I took a reading yesterday, when I unplugged the regulator. It was 12.34 volts. This morning
it shows 12.26 volts. Probably 10 hours have passed by. I'm guessing the alternator or
voltage regulator probably aren't the problem.

I've got both a digital voltmeter and an analog one.
Anybody got any ideas? If I have to pull fuses, one at a time, this could take awhile......
 
Remove the batt ground and place your V/O meter inline.
Start removing fuses till it read 0 and you have located the drain.
 
My '66 was doing that same thing until I changed out the modern radio. Seems the memory system in the radio was bad and put a constant heavy drain on the battery. Works great since I installed the new radio.
 
"Mach1Rider" said:
Remove the batt ground and place your V/O meter inline.
Start removing fuses till it read 0 and you have located the drain.
Click to expand...

Roger that; I'll try that next.
 
"AzPete" said:
My '66 was doing that same thing until I changed out the modern radio. Seems the memory system in the radio was bad and put a constant heavy drain on the battery. Works great since I installed the new radio.
Click to expand...

You know what? That's a really good point. I've got a aftermarket system in there from
Custom Autosound. Almost guaranteed to pull that fuse first. Seems like it was about the
same time I installed that item is roughly the same time I noticed a drain. (Had a factory
clock that had been converted to a quartz movement that was put in about the same
time and it initially got the blame and I pulled it and sold it on ebay- it wasn't the problem)
 
I spent a lot of years traveling all over repairing industrial equipment and learned a lot about troubleshooting alien machinery. The one troubleshooting tip I learned invaluable and share with everyone is usually the most productive:

Ask yourself (them) what was the last thing you (they) did before the problem developed? If they say "nothing"...ask again. Lots of times you have to probe a bit more to get the clean answer but when you finally get there you will many times find out what was done to mess things up.

Put into automotive example it's like the guy whose car "isn't running right". He'll typically tell you it just out of no where started to act up. Ask enough of the right questions before you open your toolbox and the answer will reveal itself. He'll say he just "gave it a tune-up". In that example, my money is on a couple switched plug wires or any other simple thing he probably messed up.

It's so common that we overlook the obvious that you have to condition yourself to start there.
 
As sensible as that advice is, I hope to $%## that's not it.
Outside the stereo and a retrotach the only other thing done was Edelbrock Pro-Flo FI.
Hopefully the latter doesn't have anything to do with the electrical drain :cry
I guess I'll burn that bridge when I get to it....
 
When connecting the DVM in line with the battery (use negative side!), be sure and set the DVM to DC current.

When working on Pete's POS, we spent at least an hour and a half stewing on the results and isolating things down. On his car, the Garmin used 50 mA, the volt-meter was another 50 mA, and the radio was still another 50 mA. All total, we saw 158 mA, which is an order of magnitude higher than what one should see. 158mA corresponds to about 8 amp-hours, and a good battery may have 200 amp-hours or more. Some batteries are less. Batteries are rated for cold cranking amps (typically 450-650 or more amps), not necessarily for amp-hours. Pete's battery appeared to have something on the order of 100 amp-hours. For his car, 3 days of not being used was enough to stop it from started.
 
Negative cable removed- inline between the negative terminal and the negative cable, set on
the 200m scale, it reads 27.2
I'm ASSuming "M" is milliamps? So 27.2 milliamps? (.027 Amps?)
 
That sounds right. 27 mA is a good reading! That indicates no significant drain.
 
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