# Generator light



## firecatsrt (Sep 15, 2008)

What triggers this light to go on?

When I hook up my battery the light comes on, ignition is in the off position. Car starts fine, etc but the light is going to drain my battery if I keep it hooked up.


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## 05GTO (Oct 6, 2004)

I had a bad voltage regulator on my 66 and the light would come on during idle. I don't remember if the light was on when the switch was off.


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## firecatsrt (Sep 15, 2008)

Well everything is new under the hood (complete turnkey motor), so I was thinking I didn't hook up a wire or something. My autometer volt gauge is showing it is charging correctly, etc. if there isn't anything wrong and I can just splice in a switch or just plain cut a wire to stop the battery drain that would be wonderful.


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## Rukee (Feb 8, 2007)

'72 I think was internally regualted, does the alternator have a 2 wire plug on top of it besides the 1 big red wire? If so, unplug that 2 wire plug and see if the light goes off, if it does it's a bad alternator.


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## 05GTO (Oct 6, 2004)

Rukee said:


> '72 I think was internally regualted, does the alternator have a 2 wire plug on top of it besides the 1 big red wire? If so, unplug that 2 wire plug and see if the light goes off, if it does it's a bad alternator.


Thanks, I was not sure when they changed to internal,


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## firecatsrt (Sep 15, 2008)

It's a 71, but does have a 2 wire clip along with the power wire that plugs into the alternator. The alternator is brand new, part of the march serpentine setup I have on the motor. I really hope that's not the problem.


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## 1970 Lemans (Jul 25, 2009)

According to the '70 Pontiac shop manual, if the generator light stays on when the ignition is off, it is due to a faulty internal alternator diiode. I had the exact same problem a few years ago. 

I replaced the alternator and that resolve the problem.


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## AlaGreyGoat (Jul 6, 2006)

From the drawing I had on the internal regulated alternator, shows the positive side of the
light going to the ign switch. It is only hot, if the switch is on. The negative side of the
light goes to the alternator plug. If the alternator is charging, then there is positive charge there
and positive on both sides of the light keeps it off. If the alternator is not charging or bad, then
there is a negative charge there, and the light will come on.
If the light is on when the switch is off, the light is being powered from another source,
not the ign switch.
Also, to excite or start the alternator charging, there must be voltage from the ign switch through the
bulb and to the alternator. On some early applications, if the bulb blows, the alternator will not charge.
Later models had a bypass resistor linked around the bulb to supply the voltage if the bulb burns out.
Once the alternator starts charging, you can remove the
light circuit, and it will keep charging, until you stop the motor.

Larry


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## Too Many Projects (Nov 15, 2008)

If you are using an internally regulated alt on a car that originally had an external regulator, you need the adapter harness to eliminate the external reg. It will plug into the original harness at the regulator location. This conversion also requires the use of the adapter harness to accept the internal alt, but I assume you must have that to get the wires to attach to the alt now. GreyGoat is correct; there is power at the indicator light at all times and needs a ground thru the alt/reg circuit to come on. Something is grounding that needs to be corrected.


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## firecatsrt (Sep 15, 2008)

Ok, I'll have to take a better look at it this weekend. This car has been a fun project, but little things keep coming up. 

It was my grandfathers since '73, no clue where the original motor is, he put in a 400 sbc out of a 60's impala which means he cut and re welded on new motor mounts, etc. To try to keep things simple I went with a sbc crate 383 stroker so that I wouldn't have to change things back and find a poncho motor, etc. As soon as I get one thing figured out there's another issue or thing he changed, I have to figure out where he got it from and go from there. Thank you guys for all your help, I am sure I'll have more questions before I drive this thing out of the garage.


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## firecatsrt (Sep 15, 2008)

well I pulled the plug off the alternator and the light went out  going to pull off the alternator now and bring it in to test it.


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