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GEN Light on

Old 12-01-2018, 01:18 PM
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IvanoMan
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Default GEN Light on

Hello
Just bring back my 1977 vette from the mechanic for breack check and now the GEN light ramain on after the engine is started.
I don't think is related to the job made on the break.
Any suggestion ?
Thanks
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Old 12-01-2018, 01:27 PM
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dar322
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Low battery? Take it for a ride. How many amps is your alternator? Low amps could cause Gen lite to illuminate.
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Old 12-02-2018, 08:19 AM
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Originally Posted by IvanoMan View Post
Hello
Just bring back my 1977 vette from the mechanic for breack check and now the GEN light ramain on after the engine is started.
I don't think is related to the job made on the break.
Any suggestion ?
Thanks
Several things to look at:
1) What does your voltmeter read? If it is straight up, pointing at 13, and remains so as the engine continues to run, your alternator is supplying current to the system.
2) Look at your alternator. There should be an 18/20 gauge brown (or possibly white) wire attached to it. This wire goes back to the plug in back of your center gauge cluster, and then to the GEN light. It performs 2 functions - a) it excites the alternator when starting, and b) Warns you when the oltage at the alternator is less than the voltage in the battery. If it is disconnected, your GEN light will come on.
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IvanoMan (12-02-2018)
Old 12-02-2018, 08:46 AM
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Originally Posted by Rotonda View Post
Several things to look at:
1) What does your voltmeter read? If it is straight up, pointing at 13, and remains so as the engine continues to run, your alternator is supplying current to the system.
2) Look at your alternator. There should be an 18/20 gauge brown (or possibly white) wire attached to it. This wire goes back to the plug in back of your center gauge cluster, and then to the GEN light. It performs 2 functions - a) it excites the alternator when starting, and b) Warns you when the oltage at the alternator is less than the voltage in the battery. If it is disconnected, your GEN light will come on.

This^^^^^^^

I doubt that the alternator just failed at the mechanic BUT it could. More likely the mechanic touched a wire ^^^^^^ causing the Gen light to illuminate
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Old 12-02-2018, 10:43 AM
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This problem can be a real hassle. I've had it many times in the past, chasing different things. I eventually sent it in to a mechanic(which takes a lot for me), he put on a self exciting alternator, never had the problem again.
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Old 12-02-2018, 01:06 PM
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Thanks for the suggestions ,
Just cheked and the cable are connected.
Double checked with hand unplug and plug again.
The red light is still there.
The volts gauge indicate 13V
mmmm.
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Old 12-02-2018, 02:26 PM
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Originally Posted by Doug1 View Post
This problem can be a real hassle. I've had it many times in the past, chasing different things. I eventually sent it in to a mechanic(which takes a lot for me), he put on a self exciting alternator, never had the problem again.
Hi Doug,
Do you have a link to the self exciting alternator?
What does it mean self exciting?
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Old 12-02-2018, 02:29 PM
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Originally Posted by IvanoMan View Post
Thanks for the suggestions ,
Just cheked and the cable are connected.
Double checked with hand unplug and plug again.
The red light is still there.
The volts gauge indicate 13V
mmmm.
Have it tested.
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Old 12-02-2018, 02:30 PM
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Originally Posted by Doug1 View Post
This problem can be a real hassle. I've had it many times in the past, chasing different things. I eventually sent it in to a mechanic(which takes a lot for me), he put on a self exciting alternator, never had the problem again.
Because a one wire alternator circumvents the light.
He didnt fix it, he bypassed it.
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Old 12-02-2018, 02:34 PM
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I suspect that it is associated with the job on the brakes; not definitely, from my experience of messing with things. If your alternator is putting out 13 VDC then the is charging (assuming your battery terminal voltage when off is about 12 VDC). but it really should be maintaining closer to 14 VDC

What was he doing to the brakes? Perhaps we can narrow down the search area.

Last edited by carriljc; 12-09-2018 at 09:24 AM. Reason: Added bold text --
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Old 12-02-2018, 03:52 PM
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Originally Posted by carriljc View Post
I suspect that it is associated with the job on the brakes; not definitely, from my experience of messing with things. If your alternator is putting out 13 VDC then it is charging (assuming your battery terminal voltage when off is about 12 VDC).

What was he doing to the brakes? Perhaps we can narrow down the search area.
He has revised the brake calipers
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Old 12-02-2018, 04:05 PM
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put a volt meter on the battery
1. sitting,key off

2.running at idle

3.running at fast idle 1500 rpm's

what are you getting for volts?
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Old 12-02-2018, 05:28 PM
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Could be a fuse ?
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Old 12-04-2018, 03:16 PM
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The alternator should put out at least 14.2 volts not 13. Check it running across the battery. You can bypass the regulator to make it energize.

Last edited by Gunfighter13; 12-04-2018 at 03:59 PM.
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Old 12-04-2018, 03:36 PM
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Originally Posted by Gunfighter13 View Post
The alternator should put out at lest 14.2 volts not 13. Check it running across the battery. You can bypass the regulator to make it energize.
Generally 14.2-14.4 with no load except charging the battery.

No less than 13.8 volts generally under load.

A fully charged battery under no load could be as low as 13.2-13.4...........

Much depends on the alternator type, revs, load, etc........

There really is no set number...except it should be more than 13 volts generally....

Last edited by jb78L-82; 12-04-2018 at 03:36 PM.
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Old 12-05-2018, 05:37 PM
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Originally Posted by IvanoMan View Post
Hi Doug,
Do you have a link to the self exciting alternator?
What does it mean self exciting?
It means that it's putting out proper voltage as soon as it starts spinning without being told anything from dash. I can easily monitor if it is working with the voltmeter on dash. Never had the light come on and it always charges strong.

here's a link. Much better price than the one I just got for my 02 vette, it was $380 on amazon. C5 needs to have the internal circuitry to communicate with the PCM.
Amazon Amazon

Last edited by Doug1; 12-05-2018 at 07:13 PM.
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Old 12-05-2018, 05:41 PM
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Originally Posted by IvanoMan View Post
Could be a fuse ?
I believe so, it's been so long since I had this problem, like I said, it was just a huge PITA. It would also be intermittent. That self exciting alternator was the best thing I ever did.
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Old 12-05-2018, 05:54 PM
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Originally Posted by carriljc View Post
I suspect that it is associated with the job on the brakes; not definitely, from my experience of messing with things. If your alternator is putting out 13 VDC then it is charging (assuming your battery terminal voltage when off is about 12 VDC).

What was he doing to the brakes? Perhaps we can narrow down the search area.
Total coincidence, doing the brakes shouldn't have anything to do with this problem. Like I said in a previous post, it was intermittent and drove me crazy. The electrical system on my car still drives me crazy, but not the gen light anymore, lol.
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Old 12-05-2018, 06:01 PM
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Originally Posted by Doug1 View Post
I believe so, it's been so long since I had this problem, like I said, it was just a huge PITA. It would also be intermittent. That self exciting alternator was the best thing I ever did.
Do you remebmer which fuse is ?
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Old 12-05-2018, 08:36 PM
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Originally Posted by IvanoMan View Post
Do you remebmer which fuse is ?
Please check the voltage with the engine running at an idle. The standard is 1 volt over battery voltage. A fully charged battery is 12.6 volts, so your minimum voltage should be 13.6 volts.
Voltage is just part of the electrical output, the other measurement is amperage. The alternator could be putting out voltage but not sufficient amperage. If you do as previously suggested and have the unit tested at Autozone they will tell you if it's performing properly. After checking all of the wire connections, and broken wires, testing the alternator would be next on the list
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