w30 gen Light issue-annoying mostly - ClassicOldsmobile.com


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Old August 12th, 2017, 10:40 AM   #1
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w30 gen Light issue-annoying mostly

So I just got this 1970 W30 in the spring, so not 100% familiar with it yet.
History is it's all factory original never been modified, except for a stereo & ham radio system the previous owner had installed, but I have completely removed. Wiring harness was stand-alone, and the original harness was not touched. And,HEI was added by previous owner who is a retired mechanic.
Properly wired thru the fuse block at the firewall.

Lately, after the car has been sitting for a few days, I go to start it and the GEN light is on full in the left gauge pod. (factory rally gauges). At first I thought the alternator had finally given up after all these years, so I replaced it with a new unit. This didn't solve the problem as I thought it would, so I delved a little further.
I disconnected the alternator field connection to see it it made any difference.
When disconnected the alternator free-wheels and when reconnected you can hear the alternator bear down, so I know its charging, but the GEN light would stay on. So, at this point I wanted to be double sure of this by disconnecting the battery while the car is running by pulling off the positive cable from the battery post. (factory clamp cables) The car remained running without the cable connected. I reconnected the cable while car running and got the usual spark over the battery terminal. As soon as this spark occurs the GEN light goes out and stays out for the day or two the car is used.
Let the car sit for a week and the same GEN light problem comes back. Disconnect and reconnect the positive cable while car running and GEN light goes out again for days of use.

My question is do you think this is a battery cable connection problem (the cable connections have been cleaned and greased for good contact) or is there another connection upstream of the battery that is being triggered by the disconnect/reconnect process?

FYI...this uses an internal regulated alternator.

Thanks in advance for any advice.
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Old August 12th, 2017, 12:02 PM   #2
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No answer about your problem but did you keep the original alternator? If not you should go back and get it if you turned it in as a core.
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Old August 12th, 2017, 04:37 PM   #3
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No answer about your problem but did you keep the original alternator? If not you should go back and get it if you turned it in as a core.
yes, the original open face altenator is in a box and still works. no way i'm turning in that as a core.
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Old August 12th, 2017, 08:21 PM   #4
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good, I can sleep tonight. I had a few places lose a few parts over the years, no fun.
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Old August 13th, 2017, 06:42 AM   #5
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The gen light is off when there is 12v on both sides of the indicator light. It will light when there is a differential between the output of the alternator and the battery voltage it sees from the ignition switch. It can light if the alternator is putting out too much or too little voltage. Have you measured the voltage at the battery with the car off and when running?
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Old August 13th, 2017, 04:00 PM   #6
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It can light if the alternator is putting out too much or too little voltage.
While this is a good point, the differential between the FIELD terminal on the alternator and the BATT terminal would need to be over 7-8 volts for the light to come on. I can't envision a failure mode where the FIELD terminal would be putting out 20+ volts.
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Old August 14th, 2017, 05:59 AM   #7
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The gen light is off when there is 12v on both sides of the indicator light. It will light when there is a differential between the output of the alternator and the battery voltage it sees from the ignition switch. It can light if the alternator is putting out too much or too little voltage. Have you measured the voltage at the battery with the car off and when running?
Thanks for the advice
Haven't had time to measure it yet, but now I know to do so.
What range should I be looking for (Car on/ Car off)?
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Old August 14th, 2017, 07:19 AM   #8
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Should have 13 plus volts running, maybe the battery is going bad.
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Old August 14th, 2017, 07:23 AM   #9
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Should be 13.8-14.2 running and 12.6 off.
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