[awsm502]

Hello Everyone,

I am building a cheap race car out of a 72 Chevelle. I plan on running with the original style external regulatated alternator for now. I have gutted the interior, and am installing a switch pannel with start button. I will not be using any of the original under dash wiring.

My question is, is it OK not to hook up the Brown wire from the voltage regulator? My understanding is that it is only for the Alt warning lamp. Does it serve some other purpose?

I am feeding my switch pannel from my trunk mounted cut-off switch, so the ignition circuit will no longer be fed by the fuse block.

Will the Alternator/Regulator be damaged by having an open circuit on the Brown wire?

How does the Brown wire trigger the Alt. Light? If the Alt is not butting out amperage, how does it send voltage through the brown wire to turn on the light?

Any help would be appreciated.

Thanks!

Keith

[undee70ss]

Originally Posted by awsm502

My question is, is it OK not to hook up the Brown wire from the voltage regulator? My understanding is that it is only for the Alt warning lamp. Does it serve some other purpose?

Yes it does. It supplies power to the voltage reg (switched power, only when key is on)

Originally Posted by awsm502

Will the Alternator/Regulator be damaged by having an open circuit on the Brown wire?

No, but you won't have any output from the alternator either.

Originally Posted by awsm502

How does the Brown wire trigger the Alt. Light? If the Alt is not butting out amperage, how does it send voltage through the brown wire to turn on the light?

Any help would be appreciated.

Thanks!

Keith

This was written by another member, a very good write up on how it works and how to troubleshoot a externally regulated charging system.

Originally Posted by Peter F

I dug this out from before, hopefully it help. If not, just post or send me your questions.

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.

Peter

[awsm502]

Thanks!

So, if I understand correctly, if I do not use a warning light, I should connect the Brown wire (terminal 4) to 12V Ign?

Keith

[awsm502]

Guys,

As I think about this more, how does the stock system keep from backfeeding 12V battery to the Ign circuit when the key is turned off? Do I need to wire in a diode on the wire feeding terminal 4?

Thanks!

Keith

[undee70ss]

Originally Posted by awsm502

Thanks!

So, if I understand correctly, if I do not use a warning light, I should connect the Brown wire (terminal 4) to 12V Ign?

Keith

NO!!! It should not have direct 12v. There has to be resistance in the circuit, that comes from the GEN bulb and/or bypass wire

Guys,

Originally Posted by awsm502

As I think about this more, how does the stock system keep from backfeeding 12V battery to the Ign circuit when the key is turned off? Do I need to wire in a diode on the wire feeding terminal 4?

Thanks!

Keith

The stock system..... the GEN bulb is fed from the IGN switch, the GROUND side of The GEN bulb goes to terminal 4 at voltage regulator. (brown wire) When the key is on and car not running, brown wire is grounded at voltage regulator, lighting GEN bulb. When car is running (and you have sufficient alternator output) power is applied to brown wire from voltage regulator, with power on both side of bulb, light goes out. There is also a bypass wire (this is a resistor wire which limits current) in case the GEN bulb burns out, or if it is a original gauge car which has no GEN light. It is there to keep the charging system working if GEN bulb burns out.

The GEN bulb and bypass wire limit current, this prevents backfeeding anything. Generally, the only time you need a diode is if you are using a aftermarket ignition box, like a MSD 6AL as it takes very little power to turn it on.

[awsm502]

OK guys, now I am confused.

I do not plan on running a Gen light. I will not be running any of the stock underdash harness. That said, do I need to hook up the brown wire at all? Or do I run a 12V Ign wire to it, with a resistor installed.

If so, any idea what size resistor? Then, I would go from the voltage reg. #4 pin, through a resister, then to a 12V Ign source?

On a stock gauge car, with no Gen light, is the resistance wire linked directly to the ignition switch?

The 72 Assembly Manual does not have a freaking schematic!!

Thanks!

Keith

[undee70ss]

Originally Posted by awsm502

;1729782]OK guys, now I am confused.

I do not plan on running a Gen light. I will not be running any of the stock underdash harness. That said, do I need to hook up the brown wire at all?

Yes, if you want the original charging system to work.

Originally Posted by awsm502

Or do I run a 12V Ign wire to it, with a resistor installed.

Correct.

Originally Posted by awsm502

If so, any idea what size resistor? Then, I would go from the voltage reg. #4 pin, through a resister, then to a 12V Ign source?

35-50 ohms.

Originally Posted by awsm502

On a stock gauge car, with no Gen light, is the resistance wire linked directly to the ignition switch? Keith

Yes

[awsm502]

Thanks Everyone!

Hopefully, this helped some others too.

Keith