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Spent some time this weekend isolating a couple grounds on a friend's 68 Camaro and wanted to post what we learned for future reference. Since grounds can be a real bear to nail down some times I thought I'd post what we learned.

Recommended tools: 10A capacity amp-meter, spare butt connectors, male/female spade connectors, wire strippers/crimpers.

Backround: This car had a history of running the battery down over the period of a couple days. The battery would be charged up from driving over the weekend and would be completely dead after sitting for just a few days.

To start we disconnected the neg battery cable and charged the battery.

Then we tried what I call a "scratch test" by touching the negative cable to the battery post. We saw some small sparks which indicated a ground, if there had been any large sparks I would be concerned with a dead short and would not use to the ammeter. Then we connected the Ammeter between the battery cable and the battery post which read 505 mA (that's a 1/2 Amp drain on the battery with nothing on).

NOTE: most Ammeters have a 10A setting that is fused. Start at the 10A setting for minor grounds and work to a lower scale. If the draw is over 10A most Ammeters have a built in fuse that will blow. A dead short may hurt your meter so be careful (that's why I do the "scratch test" LOL).

The first step we tried was to remove extra wiring added to the connections on the fuse box one at a time. We quickly found a connection at the top of the fuse box that was powering the electric gauges and was not switched on/off by the ignition. Current draw reduced to 275 mA after this was disconnected and we rewired it to a switched power source.

Then we removed each fuse one at a time (including in-line fuses in the engine compartment) and observed no further drop in the 275 mA draw.

Then we turned our efforts to the engine compartment wiring harness. There is a junction block behind the battery that provides power to the headlights and any other "extras" that have been wired straight to the battery (stereo amps, MSD power, electric fans, horns that play Dixie, etc).

When we disconnected the main red wire from the block our drain dropped to zero, so we knew that there was something unfused that was killing our battery. We cut the main power wire to the MSD and respliced when that didn't stop our drain. Then we unplugged the alternator (not the output wire) which stopped the drain.

We finally determined that the two-wire alternator plug was wired backwards. The alternator still charged even with the plug backwards but it also drained the battery with the car off.

After rewiring the alternator and electric gauges our current drain on the batery was down to 2.2 mA (that's 1/500th of an amp). This small of a drain is normal IMO and could be the result of electronics that require unswitched power for memory.

Hope this helps . . .
 

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Eric,

"Scratch testing" around the car battery is never a good idea. You got away with it, but that's not guaranteed!! During the charging process, batteries create a lot of explosive hydrogen gas. It doesn't take much of a spark to ignite it! I've seen more than one guy get a face full of exploding battery while scratch testing or jumping another car.

The safer way to do this is to remove the ground cable and connect a 12V test light to the negative post. Probe a good ground some distance from the battery (engine block??) and see if the test light illuminates. If it lights, you have a pretty serious draw and you can start pulling fuses etc... until you find the short circuit. I've actually modified one of my test lights with a bulb that draws a good solid 1 Amp. I find this works great for big shorts. It's also great for finding those dirty connections that a Volt meter will miss.

Just my $.02

Paul D.
 

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Excellent example of the "seek and destroy" technique Eric. Procedures like that will solve almost any electrical problem. Multimeters are a must. Although those first gen schematics can be a bit tough to read not having one is like traveling without a map - (you only know where you are if you've been there before). I'm sure Paul didn't mean to poo poo your story, but you did dodge a bullet with the scratch test near the battery. A test lamp between the battery post and clamp is also a good way although it doesn't seem that high tech. The good thing about test lamps is that they current regulate. You could have a dead short and the test lamp would illuminate full brightness but not cause a fire or flow that &$%[email protected] fuse.
 

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Good investigative work, Eric. A good multimeter is a must.

This is probably the reason others here have a discharged battery and both units, reg & alt, checked good at the store, and they have pulled all the fuses and haven't found anything wrong.

Hope others can remember this fix.

I probably would have done the same trick with the battery clamp, very light discharge, open hood, a breeze blowing, maybe, as long as I didn't smell the gases, sure, why not?
 

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Yup, didn't mean to wiz on your parade Eric!! Nice job finding the source of the problems!!


Just wanted to remind everyone that we sometimes get too complacent around dangerous things!! I know we're all occasionally guilty of it, but it's just not a great idea to make sparks anywhere around cars!!

Paul D.
 

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Discussion Starter #6
Good point about the hydrogen . . . safety is an important consideration. You typically get a few sparks when disconnecting the cable anyway :eek: so its a good idea to make sure the hood has been open a while before trying to disconnect anything. Its never fun to play around batteries especially when you know something is wrong.

Another good safety pointer when working around batteries is to always remove any jewelry. I burned the you-know-what out of my wrist last winter when my watch band arced across the battery post :eek: Still have scars . . . but at least my watch still works
 
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