My '72 has developed a battery drain. This is what I've found...
With a volt meter hooked between the battery pos post and the positive battery cable, the meter shows a full 12+V current flow.
With the 2 wire connector unplugged from the back of the alternator (internal reg), the meter then drops to zero.
I had thought the alternator had gone bad so I replaced it...same symptoms.
This drain will kill the battery within one day is left sitting.
Any ideas?? TIA!

Bill,
i have always used the negative battery cable for this test.
don't know if it makes a difference.

david

Either the wires are reversed or another bad alt. Something to check... on the 2 wire connector, one wire should only have 12 volts with key on, none with key off, the other has 12 volts all the time. If they both have power all the time, the problem is elsewhere.

You can always use your tester between the meter and negative cable, then start pulling fuses and see if you can isolate the problem that way. If you hit the right circuit when pulling the fuse and the meter drops, you'll know where the issue lies.

Something to check... on the 2 wire connector, one wire should only have 12 volts with key on, none with key off, the other has 12 volts all the time.
Checked this today when I got home...it is as you have noted. #1 wire is hot all the time; #2 wire only with key on.
I also double checked again to verify...current flows from the battery only when these two wires are plugged into the alternator. If I unplug, the current stops. :confused:
I also checked these two wires when plugged into the alternator...as it should be; one wire hot/key off...both wires hot/key on.
Could I possibly have another bad alternator?
The car has been converted over to an internal regulator but ran fine until recently.
Thanks for all the suggestions.
Bill

you cannot see if you have a draw on your battery by putting a meter on the + side of your battery. The meter has to be between the - side of battery and the ground. After the meter is hooked up and you see you have a draw start disconnecting one thing at a time to find where the draw is coming from. have fun Jon

You can check for an existing parasitic drain on either the positive or negative side of the battery but volt meters are really supposed to be connected in parallel, not in series.
You really need to use an amp meter that measures milliamps but a test light works, just doesn't show how much.

Seems to me if unplugging the alternator makes the drain go away, the problem has to be there.
Is the GEN light still being used?

I also checked these two wires when plugged into the alternator...as it should be; one wire hot/key off...both wires hot/key on.
Could I possibly have another bad alternator?
Checked this today when I got home...it is as you have noted. #1 wire is hot all the time; #2 wire only with key on.
I also double checked again to verify...current flows from the battery only when these two wires are plugged into the alternator. If I unplug, the current stops. :confused:

Are you sure you don't have the wires reversed? Who did the conversion? Most conversion instructions usually go by wire colors, using the blue for the light and the white for the sense, but you can swap the wires and it will still work (white for the light and blue for the sense) The brown wire at the old external voltage regulator is for the light, it must end up at terminal #1 at the alternator. I usually refer to the terminals. The wire from the GEN light, which is only hot with the key on, goes to #1 terminal at the alternator. This is usually closest to the BAT terminal. The sense wire, which is hot all the time, and comes from either the main splice, horn relay or alternator BAT terminal (depending on how it was converted) goes to the #2 terminal at the alternator. There are markings on the back of the alternator to show which terminal is which, see pic

http://www.chevelles.com/showroom/data/500/Alternator1.jpg

If the wires were reversed, the alternator would still charge fine, you would just have a drain when it would not be running.

The car has been converted over to an internal regulator but ran fine until recently.
Thanks for all the suggestions.
Bill

How often was the car driven? It is possible that if it was driven often enough, the battery would never go dead. If it normally sat for a while and was fine, the wiring was probably correct, but it doesn't hurt to check.

Thanks Greg for the details.
I did the internal reg conversion about 2 months ago after the original external reg stuck and boiled a battery. The car is not a daily driver but is driven often on weekends.
My conversion procedure...
Clipped off all 4 wires on the plug to the regulator. Spliced #1 and #4 wires together. Capped off #2 and #3.
Then, purchased a new plug for the internal alternator, ran #1 wire on it to the 12v post on the back of the alt, #2 wire spliced to the blue wire in the car's harness.
I'll need to double check tonight when I get home. From reading your post, it sounds like I've got the alternator plug wired backwards... :clonk:

You must have did the type of conversion posted here
http://www.chevelles.com/techref/ftecref14.html
This makes the alternator work something like a one wire alternator (voltage is sensed at alternator BAT terminal. It is fine if the car doesn't have any high draw idems.

http://www.chevelles.com/techref/tr14ab.gif

http://www.chevelles.com/techref/tr14b.gif

Another way of doing it, senses at the main splice, and also uses the white wire (also applies to 10si's too) Better if there are higher draw idems.

http://www.chevelles.com/showroom/data/500/alternator_wiring_pic2.JPG

If you had the wiring correct, most likely a bad alternator.

Well, I checked all my connections and the internal/external conversion I did previously is correct.
Bad news is, now there is no more battery drain. I went to start testing the seperate circuits and there is no current flow! Its' been all hooked up for over a day and the battery is still fully charged. :confused:
I hate intermittent problems!
Thanks for y'alls help!! :thumbsup:

Well, I checked all my connections and the internal/external conversion I did previously is correct.
Bad news is, now there is no more battery drain. I went to start testing the separate circuits and there is no current flow! Its' been all hooked up for over a day and the battery is still fully charged. :confused:
I hate intermittent problems!
Thanks for y'alls help!! :thumbsup:
Has the car had any wiring done or add ons? If the problem shows up again, don't touch anything and test, it could be a backfeeding problem. You would know this by things that normally don't work with the key off (like turn signals) suddenly do. Something to look out for.