Alt power when key is off

[72tutone]

Gents, I have something draining my battery. Ive done some searching and found some possibilities but not my particular case
I purchased the wiring pigtail to convert from an external to a cs130 style alternator.
I seem to be running into an issue when the key is off, im seeing 12 volts to the power on the alt.

Is this normal? I wouldnt think so. Because something seems to be draining power.

[kwmech]

12v to alt with key off is normal.

[davepl]

That's normal, I believe. But if your alternator had a bad diode, it can drain the battery (backwards). If you unplug the alternator, does the drain go away?

You can test for this with an ammeter or voltmeter at the battery (between the battery and the post when the key is off).

[72tutone]

Thanks for the info guys.

When you say test between battery and post when the alt is disconnected are you referring to the post on the alt?

Also, I noticed with key on, or acc and the motor isnt running the alternator is letting out a small hum noise. You can hear it noticeably if you stick you ear up to it.

[davepl]

Originally Posted by 72tutone

Thanks for the info guys.

When you say test between battery and post when the alt is disconnected are you referring to the post on the alt?

Also, I noticed with key on, or acc and the motor isnt running the alternator is letting out a small hum noise. You can hear it noticeably if you stick you ear up to it.

I mean you could run your ammeter inline:

BAT + Ammeter + Cable

or run it as a volt meter, it'll show you the potential voltage, roughly the same idea.

I think you should likely pull the alternator and head down to your local auto parts store to get it tested. Cheap and easy to do, and it's sounding a little suspicious.

[old Chevy guy]

Where did you get that pigtail in the picture? Tell me more about what's going on with that?

[72tutone]

The pigtail I purchased was from classic parts of america. Basically its an alternator conversion wiring harness

http://www.classicparts.com/1963-72-.../#.VzS0wL7kA3g

They sell these at alot of different places. Basically you hook your existing connections to this pigtail. One goes into the existing alt plug, the other goes into the harness that would normally plug into your external voltage regulator.

Lots of guys on here have manually done this via looping/jumping the connector harness that plugs into their external regulator. I was just lazy and purchased this one.

[VetteVet]

Originally Posted by 72tutone

The pigtail I purchased was from classic parts of america. Basically its an alternator conversion wiring harness

http://www.classicparts.com/1963-72-.../#.VzS0wL7kA3g

They sell these at alot of different places. Basically you hook your existing connections to this pigtail. One goes into the existing alt plug, the other goes into the harness that would normally plug into your external voltage regulator.

Lots of guys on here have manually done this via looping/jumping the connector harness that plugs into their external regulator. I was just lazy and purchased this one.

What you need to do is start at the plug that plugs into the external regulator.
Unplug it from the CS harness and check the brown wire for voltage.
key off ----0 volts-----key on 12 volts
Red wire ----12 volts constant

What the block you plug the EVR plug into is just a jumper that jumps the brown wire to the white wire and the red wire to the blue wire. Then the blue and white wire runs through the harness to the alternator conversion harness that you bought.

The white wire will plug into the conversion harness to the wire that goes to
the L terminal on the alternator. It should have a resistor in it, about 80 ohms. They can vary a lot but anything between 35 and 300 ohms should work. It should measure 0 off, 12 on. as well, since it is just an extension of the brown wire.

The blue wire will plug into the wire in the conversion harness that goes to the S terminal (probably the red wire) This wire should be constant 12 volts.

The large wire on the back of the alternator is the charging wire and it is connected to the battery positive so it will be constant hot.


Here is a picture of the conversion. This is for the SI alternators but the jumpers are the same. Except the resistor is not needed with the SI it only requires a 10 ohm resistor which is already in the truck harness.



This is the CS conversion that I drew up which is much easier even though it does the same thing.

[72tutone]

Thanks VetteVet
I do have 12 on on the brown with key and 0 with off
12 on red constant regardless.
Looking at my setup I have the blue and white going to the original pigtail which then the adapter plugs into and then to the alternator.
The red is going to the hot on the alt.

However... I do see a 12B going to the alt. I dont have a common ground running to the alternator. As a matter of fact there isnt a connection or hookup for it anywhere. I see in your diagram you have a 12B running into a common ground via sheet metal.
So should I omit this connector?

[VetteVet]

Originally Posted by 72tutone

Thanks VetteVet
I do have 12 on on the brown with key and 0 with off
12 on red constant regardless.
Looking at my setup I have the blue and white going to the original pigtail which then the adapter plugs into and then to the alternator.
The red is going to the hot on the alt.

However... I do see a 12B going to the alt. I dont have a common ground running to the alternator. As a matter of fact there isnt a connection or hookup for it anywhere. I see in your diagram you have a 12B running into a common ground via sheet metal.
So should I omit this connector?

You can disregard the black wire as it is only needed to ground the EVR and the alternator together and to ground the regulator to the chassis. The CS is grounded to the block and doesn't require an external ground.

Can you verify that the brown white L terminal path is correct and the red blue and S terminal path is correct. If the adapter plug that goes into the alternator has the wires switched they will send power to the L terminal with the key off and this will flow current through the alternator diodes to ground and will drain the battery.

In the posts above they are telling you how to check for a key off drain.
You can take the negative terminal off the battery and connect a multimeter between the two. Red lead on the battery and black lead on the cable.
With the meter set on 10 amps scale you should read less than 3 milliamps .003 with every thing off on the truck. If you read more than that you have a drain. Again be sure all the lights on the truck are off and anything else that uses battery power.

If you get a high amp draw on the meter I.E. .05, then disconnect the plug from the alternator and see if it drops. If it doesn't then disconnect the larger charging wire on the back of the alternator (remember it's hot) and see if it drops the reading. if it does then the diodes in the alternator are blown and are allowing the battery current to run through them into ground and draining the battery.