Alternator charging light

[Boise]

As long as i have owned my car the charging light has never worked. Today I tried to see if the bulb was burnt out. Bulb works fine. With the ignition switch off both wires going to the light have 12v. So essentially no ground so the light doesn't light up.

Can't figure out why its not working. Any ideas?

[Mark IV]

Do you have a "one wire" alternator? Calling Blas, the Bat Signal is lit.

[Boise]

Originally Posted by Mark IV

Do you have a "one wire" alternator? Calling Blas, the Bat Signal is lit.

I believe I do. There is only one wire going to the battery. The car does appear to have a voltage regulator on the left fender well.

[patrickt]

Snap a pic of the cover plate on the alternator that tells the name, model, etc., like Power Master, and post it. Your car might have started out as a regular alternator with an external voltage regulator that was excited by the charging light, and then along the way someone put in a one-wire alternator.

[spdbrake]

https://www.ronfrancis.com/prodinfo.asp?number=LS%2D11

https://www.summitracing.com/parts/rfw-ls11

This should do it.

[patrickt]

One wires used to be a PITA, but they're pretty nice now. When I was a kid they wouldn't work worth a crap at low RPMs, and you always had to rev them a couple of times to get them going. I don't think that holds true anymore, but I still have a 60 amp AC Delco with an external VR.

[Anthony]

Been through this recently.

How many wires coming off the alternator ?
If 1, then you need to get the above linked module.

If you have 3 wires, then the wire going to the 2 wire plug, labeled as #1, needs to wired from the ignition switch, then to the alt light bulb, then to the alternator spade labeled #1. This is the "field" wire, that needs to be energized to create a magnetic field, so the spinning alternator will create a charging voltage / current. The spade wire labeled #2, is the voltage sensing wire for the internal regulator, and is usually best connected to the fuse block hot, although many people jump it over to the Bat wire.

[patrickt]

Originally Posted by Anthony

Been through this recently...

Uhhh, like this?

[jhv48]

Plain and simple. With a one wire alternator, the light does not function.

[jacobsed]

On a Superformance where is the charging light?

[jhv48]

It’s the red light on the dash behind the steering wheel. It does not function with a one wire alternator.

[Morris]

Seems to me that if you have the one wire alternator...you could take a jumper off the alternator and go to one side of a lamp.....then on the other side of the lamp...connect to the battery......that way when you turned the ignition on you would see the lamp on from one side being hot ...then when the alternator started spinning and had a output the light would go off because you would have a 12 volt potential on both sides of the lamp....if the alternator started going bad the the battery side would be hot and the alternator side would be ground so the lamp would light.......I think ��

[jhv48]

Or, you could watch your ammeter and if it stays to the left of center, you probably have an alternator going bad.

[Gaz64]

Originally Posted by Morris

Seems to me that if you have the one wire alternator...you could take a jumper off the alternator and go to one side of a lamp.....then on the other side of the lamp...connect to the battery......that way when you turned the ignition on you would see the lamp on from one side being hot ...then when the alternator started spinning and had a output the light would go off because you would have a 12 volt potential on both sides of the lamp....if the alternator started going bad the the battery side would be hot and the alternator side would be ground so the lamp would light.......I think ��

Yes, that should work.
A bulb in parallel with the heavy lead, would show up any voltage difference, so brightest at ignition on, 12v + on one side, and 0 volts at the alternator.

The bulb would present virtually no circuit path while in parallel with near 0 ohms of the heavy charging wire.

[patrickt]

I don't think that will work -- but I have never tried it, so I really don't know. But if it was that easy, why would Tuff Stuff go to the trouble of putting this in the instructions for its 1-wire alternator?

NO WARNING LIGHT
Note that a 1-wire alternator does NOT permit the use of a charge
warning (idiot) light. Most hot rodders and muscle car enthusiasts
prefer the use of a volt meter or ammeter to monitor charging.
However, certain Tuff Stuff alternators like the 7127, 7139 and
7140 series have terminals that may be used for a warning light.
To wire a warning light using one of these alternators, simply
remove the terminal plug cover and connect the R (Left terminal,
looking from the back of the alternator) to the warning light wire.
https://www.tuffstuffperformance.com...structions.pdf

and PowerMaster says the same thing about theirs:
https://www.powermastermotorsports.com/001___IS_ALT.pdf

[Gaz64]

Looks like it would not be worth the risk.
Just do as the manufacturers have intended.

[Boise]

Originally Posted by Anthony

Been through this recently.

How many wires coming off the alternator ?
If 1, then you need to get the above linked module.

If you have 3 wires, then the wire going to the 2 wire plug, labeled as #1, needs to wired from the ignition switch, then to the alt light bulb, then to the alternator spade labeled #1. This is the "field" wire, that needs to be energized to create a magnetic field, so the spinning alternator will create a charging voltage / current. The spade wire labeled #2, is the voltage sensing wire for the internal regulator, and is usually best connected to the fuse block hot, although many people jump it over to the Bat wire.

Just one wire

[Boise]

Originally Posted by patrickt

I don't think that will work -- but I have never tried it, so I really don't know. But if it was that easy, why would Tuff Stuff go to the trouble of putting this in the instructions for its 1-wire alternator?

NO WARNING LIGHT
Note that a 1-wire alternator does NOT permit the use of a charge
warning (idiot) light. Most hot rodders and muscle car enthusiasts
prefer the use of a volt meter or ammeter to monitor charging.
However, certain Tuff Stuff alternators like the 7127, 7139 and
7140 series have terminals that may be used for a warning light.
To wire a warning light using one of these alternators, simply
remove the terminal plug cover and connect the R (Left terminal,
looking from the back of the alternator) to the warning light wire.
https://www.tuffstuffperformance.com...structions.pdf

and PowerMaster says the same thing about theirs:
https://www.powermastermotorsports.com/001___IS_ALT.pdf

The one wire alternator can be used with a functioning warning light!

So after looking around and taking some readings using the meter I figured it out. My alternator is a one wire version. The stator and field connections were unused and covered with a rubber cap. I found the black wire coming down to the alternator in the harness but still unconnected. I connected this to one of the alternator connections. Then I verified that the voltage regulator was no longer used. I had to jump the solid black and solid blue wires that go to the voltage regulator.
After that the alternator warning light works perfect! Its an easy job and works for anyone who has a single wire alternator.
Thanks for all the help

[patrickt]

Originally Posted by Boise

Thanks for all the help

... and they all lived happily ever after.