GEN light on dimly - what does it mean? - ClassicOldsmobile.com


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Old June 9th, 2018, 11:06 AM   #1  
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GEN light on dimly - what does it mean?

Hi-


I'm working on a 62 Oldsmobile F-85 with the 215 V8. The car has a generator on it. Lately, the GEN light has been coming on dimly while driving. Sometimes I don't even notice it unless it is dark enough out, or unless I look closely at it.


I have seen this on other GM cars in the past. What does this mean? Is there really a problem?


I was concerned, so I put on a new voltage regulator. This didn't change anything, so I removed the generator from the car, installed new brushes, and I lubricated the generator bearings. The generator should be in good shape.



Still, the light comes on dimly. It isn't all the time, either, maybe 50% of the time.


My question is, is there really a problem here? And, why does this happen?


I read in the service manual about some kind of fuse in the generator wiring or something, but I don't see anything like that under the hood anyplace. I thought maybe this "fuse" was blown or maybe had poor electrical contacts.


Thanks for any thoughts you may have!
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Old June 9th, 2018, 11:30 AM   #2  
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With the engine running turn on lights, radio, wipers, blower motor, etc and see if as you increase the load it gets brighter. If it does you may have a poor or corroded connection in the power circuit or a weak ground.
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Old June 11th, 2018, 05:16 PM   #3  
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This is exactly what is happening. I tested it, and the more accessories I turn on, the brighter the light gets. Interestingly, the light also gets brighter as engine speed is increased. I don't know why that would be. Thanks for the ideas - I will check these things.
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Old June 11th, 2018, 06:43 PM   #4  
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Check and clean all your red and black battery cable ends, both sides and the battery terminal also. Do the same for the ground strap at the passenger rear of engine. unplug voltage regulator and clean the connector contacts. Unplug the terminals at the alternator and make sure the plug is tight and clean. Check the connection at the back of the alternator (red wire) to make sure its clean and tight. The same wire runs to the horn relay power stud. Make sure the terminals there are clean and tight.
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Old June 11th, 2018, 08:36 PM   #5  
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Troubleshooting a Dim Gen light (NOT AT Wide Open Throttle...thats a loose fan belt)

For an internally regulated system:

The GEN bulb is supplied with +12v with the key in the RUN position. The other side of the bulb is connected to the #1 terminal on the alternator (assuming a three wire, internal regulator alt, like the SI-family). In the regulator, the #1 terminal is grounded when the alt output is low and should be full alt voltage when the alt is charging. By having the same voltage on both sides of the bulb, it does not illuminate. If voltage on one side (and it could be either side) is low, current flows through the filament and the bulb starts to glow. The greater the voltage differential, the brighter the bulb. If the bulb is glowing dimly, you have a voltage drop on one side of the bulb. Start by checking output voltage at the #1 terminal on the alternator - it should be 13.8V or so. If you can get to the IP connector or the two terminals of the bulb socket, check the voltage of each of those to ground with the engine running. They should be the same. If one is lower, find the voltage drop in that wire. It will likely be a bad ground or a dirty connector terminal someplace as Eric stated.


For an externally regulated system:

Your 62 has an external regulator and the light is fed from the regulator connector on the firewall terminal #4, I think it's a brown wire. The brown wire goes through the bulkhead connector and then directly to the light. On the other side is a pink wire that also feeds power to your fuel gauge, temp light, parking brake light, and oil pressure light. So depending on which side of the light is low (brown or pink wire to ground) that will be the direction you need to trace.
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Old June 12th, 2018, 06:01 AM   #6  
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I believe you have a generator and not an alternator. If there is a fuse it would be located on the regulator B terminal. If you have an indicator light , the light wire would be connected to the A terminal either at the regulator or generator. Have you taken any voltage readings under the different conditions? If you put in new brushes they need to be seated. The armature should have been turned on a lathe and undercut. You may have brush hop. If the brushes are not seated the brush will bounce and give the symptoms you have. Take volt readings at battery with car off, on at idle, at idle with load, at high rpm with and with out load. Post your results.
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Old June 12th, 2018, 07:59 AM   #7  
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ahhh yes stellar...I always miss the generator to alternator thing. A 62 would be a Gen not an Alt...duah. Unless its been converted?
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Old June 12th, 2018, 09:02 AM   #8  
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x2, he did say generator.
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Old June 12th, 2018, 09:24 AM   #9  
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Eric that's what I get when playing on the computer b4 bed, refrigerator eyes. Whether its a rotating or stationary field I would think the troubleshooting is still similar. The bulb illuminates when a drop is detected in either direction. So this should point in the direction of the source of the problem(voltage drop).

stellar also good info on brush hop. I have not ever seen this phenomenon in an automotive application as generators were obsolete by the time I started wrenchin.
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Old June 14th, 2018, 07:36 PM   #10  
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Thanks everyone for your detailed replies. I have some good ideas now of where to look. I haven't had a chance to work on the car the last few days, but I will very soon. Yes, the car as a generator on it. Thanks again.
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Old June 15th, 2018, 05:38 PM   #11  
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I was able to get a hold of a reliable digital volt-ohmmeter today. I found out that the generator is not charging the battery at all - the car is running on the battery alone. Not sure what to think since I rebuilt the generator and installed new brushes, and added a new voltage regulator already. But I will look for poor grounds and bad connections as many of you suggested.
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Old June 15th, 2018, 06:36 PM   #12  
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You need to figure out why the Gen is not charging. Doubt its poor grounds.
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Old June 16th, 2018, 05:23 AM   #13  
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Yep, I think so too. Thanks!
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Old June 16th, 2018, 07:48 AM   #14  
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......just my 2cents worth


Did you polish the area in a circular direction (around the diameter, NOT cross ways) where the brushes touch ? Use 600 grit lightly. There could be a glaze thats preventing good contact. Perhaps hit the brushes too.
BLOW, degrease and blow off the brushes and armature before re-assembling.


At this point, if that doesn't charge, you may need to find an electric motor winding shop or a remanufactured generator.
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Old June 16th, 2018, 02:14 PM   #15  
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No, I didn't do that. It is worth trying.
As you said, I had begun to think getting another generator is my only option.
But I will try polishing the area on the commutator first.
Thanks!
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Old June 16th, 2018, 03:52 PM   #16  
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Also clean in between the ea of the copper lands with a pick or small screw driver.
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Old June 16th, 2018, 11:20 PM   #17  
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Oldcutlass, thanks, I forgot that part. "in the old days" I used a hack saw blade that had been ground off on the end. A tooth or two is all you need to "drag out" junk.
Lets hope he gets it charging like brand new.
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Old June 19th, 2018, 12:17 PM   #18  
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Don't overlook the obvious.

Did you polarize the generator after the rebuild?

If not, that could be the cause of your problem.
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Old September 8th, 2018, 07:55 PM   #19  
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All-
I never did update you on how this project turned out.
I was able to find, online, a rebuilt generator for my car. I installed this, along with a new voltage regulator, polarized the regulator - and I'm back in business on the 62 F-85!
Thank you all for your advice and tips.

But - now, 2 1/2 months later, I have run into a similar problem with a similar car. I have a 62 Buick Skylark also. I hope you don't mind me asking about this Buick since it's basically the same car as the 62 F-85. Also has the 215 V8 and generally similar mechanical set up.
So the GEN light started coming on brightly at idle, or when decelerating. I checked, and the belt is tight, the idle speed is high enough.
Used a voltmeter, and sure enough, charging when engine is revved a bit, but at idle the voltage drops to ~12.6.
I noticed something else odd - when revved, I see a bluish-white light out the back of the generator! I don't think this is normal, is it??
So I removed the generator and took it apart. It looks almost new, like it was rebuilt before, with a new bearing. The brushes hardly look worn.
I noticed one odd thing, near the brushes, a very thin line of silver deposit on the inside of the generator housing.
I think this is a clue, but I don't know what it means.
So, I cleaned things up well inside the generator - used a pick and cleaned out the gunk between the bars on the commutator.
Also used electrical contact cleaner and cleaned things up inside.
I re-installed the generator - no change. Charges with engine revved, doesn't charge at idle.
I had a new voltage regulator on hand so I replaced that for the heck of it. Still - no change.
Does anyone have thoughts or ideas?
You had some good ones for my previous problem on the other car - but this is slightly different so I'm wondering what you think.
And the bluish white light out of the back of the generator only when revved - I really wonder if that is ok or not!!
Thanks for your thoughts!!
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Old September 9th, 2018, 04:54 AM   #20  
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You have an open armature. The silver streak is solder thrown from the armature commutator where the wires are soldered in. It was over heated for some reason. probably either overcharging or too much of a demand over an extended run.
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Old September 14th, 2018, 04:59 PM   #21  
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blue light in generator

THANK YOU for this explanation. I used a mirror and held it to the back of the generator when the engine was revved a bit.
I can see blue sparks inside the generator. I took it apart again and see that the brushes have burn marks on them. Replaced the brushes with new ones and I see that the blue light/sparks are still there. So I know that wasn't it.
I guess I need yet another generator for this car also. Wow - less than 3 months after the other car needed one.
Well, such is life.
Thanks for all of the help!!
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Old September 15th, 2018, 08:12 AM   #22  
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The armature can be resoldered.
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