Technical Alternator idiot light necessary?

Sorry guys, my memory is a little fuzzy. on a GM 3 Wire Alternator, is the idiot light on the exciter wire from the ignition necessary or can it just be wired straight? can't remember if the lamp played some role. I don't recall that it does, but just wanna double check. thanks.

 

I run exciter wire from 'on' at ignition. ALSO run a Volt meter. Curious to hear what others say about the light: All my cars are Pre-Idiot'.

 

I thought that it did, and that it had to be an LED because a diode only works in one direction, but I could be WAY wrong about that.

I would very much like to hear about proper GM 3 wire alternator wiring as I need to do this in my '57 next week. I know there was a great, simple article floating around a long time ago which I used many times but unfortunately I can't find it anymore and I can't exactly remember all the details of it.

Anyone able to post the correct wiring info would be helping out two of us.

 

The light gets power from the "ignition" side of the harness causing the alternator to charge. If there is no charging then that side goes to ground and the light comes on.

So to answer your question, there is no need for the light.

 

My memory says that the light is powered from the ignition switch, it comes on with key on, then when alternator charges it back feeds that wire to shut off the light. So I guess you don't have to hook it up, but do need some resistance in the wire to stop the back feed. But unless you have a volt meter I would think that you would want to keep it working. But you should double check. And today I also seem to type slow!!

 

I run idiots.....just because,

 

Squablow, the BAT terminal can go directly to the battery or the starter. Mine goes to the battery. The exciter wire runs to the idiot light from terminal 1 and the last wire goes to the BAT terminal from terminal 2 on the alternator.

https://www.jalopyjournal.com/forum/threads/how-do-i-wire-a-gm-3-wire-alternator.30629/

 

I keep it simple. The light makes an easy exciter wire resistor.

 

If you want a 3 wire system to work you need to hook the wire up; if you don't want the light, put a diode in the wire or the alt will back feed and the key won't turn the engine off. Accessory terminal could be used if available.

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GM used a resistor wire in series with the light bulb, on most of them. You can use a resistor, light bulb, diode, or connect it directly....your results might vary, of course.

I prefer the idiot light. If there is no factory idiot light available in the dash, I might put the light bulb at the alternator, or I might use a resistor, or a diode, depends on the car. For example, when I ran an MSD ignition in my truck, I used a resistor, and it would not shut off when turning off the key, so I added a diode. The MSD has only a "sense" wire connected to ignition, it gets it's main power from always on battery voltage. But anything that has an ignition that draws significant current through the ignition system, will shut off OK.

So, don't sweat it. Try the easiest thing, and if it works, you're good.

 

Quick reference..

 

To start charging the alternator need some voltage for the field winding's to initiate a magnetic field. And it get it from the ignition switch thru the lamp. So yes you need the lamp.
Where you put it is something else.

 

Yeah OK. That's what I though. I have an old A100 van that was rewired recently and they wired the alternator backwards. and it was causing all kinds of obvious problems. whoever wired the van did install a lamp, but it was just taped inside the harness under the doghouse.

thanks.

 

Here is a site that has some good info. http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

 

my truck hasn't had one in about 30 years, no problems.

 

Keep in mind that an ammeter won't always tell you if you're having issues with an alternator.

 

OK so big stud on the back of the alt goes to the positive terminal on the battery, or the starter lug (does it matter where?), the #2 post just gets looped around to the big stud, and the #1 post goes through an indicator light and then onto the ignition post of the ignition switch, is that all correct? If I use an LED as the indicator light, would there be a need for a separate diode (since an LED is a diode after all)? I also see a fuse in the diagram above, is that necessary? If so, what wattage should be used?

Sorry if I'm hijacking this thread kinda and also for all the questions but this is really useful info for a body guy who's not much of a mechanic and definitely not an electrical engineer.

 

Would something like this make an appropriate indicator light?

https://shop.advanceautoparts.com/p...26/6300052-p?store=1328&product_channel=local

 

hard to say, all we can tell from the description and specifications is that it's 12v. No idea if it's LED or incandescent, or how bright it is or current it draws.

But it might work.

If you use an LED, you have to wire it the right direction.

As for the rest of your post, about what to do...sounds about right. Not perfect, but good enough to work.

 

The GM style regulator will fail prematurely if you put a full 12v to the exciter...it needs to be resisted...the same resistance as a #57 bulb.


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LED’S have low to almost zero resistance and will light but not provide the needed resistance...


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So it's actually better to use an incandescent bulb as the indicator light, because it functions as a resistor as well? Is a diode also necessary when using the indicator light?

 

No it is not necessary to use a diode if the #57 bulb is used...The low resistance of LED’S is also what causes your turn signals to flash rapidly and adding resistance is the solution or change the flasher to an LED FLASHER.


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Perhaps you mean high resistance, not low resistance? Led lights that are sold as automotive indicator lamps have a series resistor in them. They draw less current than a similar brightness incandescent bulb, which means they have higher resistance.

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I have often used side marker bulb/socket, placed wherever you choose

 

I went with this.
http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

worked for me

 

I've got some of these with (what I think is) a 194 bulb in it, I looked up the specs on the 194 bulb but I can't find specs on the 97 bulb to see if they have similar resistance, but I would assume they do, would this work better for my indicator light? I've got lots of bulb sockets for older style bulbs but they just have the one wire and I assume the bulb needs to be inline and insulated from ground so those won't work, correct?

The bulb I would think would also be an effective fuse, so big alternator stud to the positive battery, #2 post looped around to the big stud, and #1 post through this bulb to the ignition terminal on the ignition switch and it should work, correct?

 

You can see by the date on this info...2002...that this info is old and the technology available in today’s world is considerably different...with the advent of the CS130 Delco alternator almost every item listed in this out of date info is invalid. More-over the next generation of Denso alternators provides another up-wards level of high output at low RPM with exceptional service.


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Yes, or you can run #2 to the Starter solenoid to give the alternator a “remote” voltage sense.


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And yes, a #194 bulb will work also...


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