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Discussion Starter · #1 ·
New alternator in my 57 Bel Air. Doesn't seem to be charging the battery. Car runs fine, and starts right up if jumped or battery put on external charger. Before I go chasing gremlins- did I read somewhere that if the GEN light is burnt out then the alternator won't charge things? My Gen light doesn't come on anymore.
 

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1956 chevy 210 del rey sedan
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if the gen light doesn't work the internal regulator in the alt is probably bad. the gen light gets 12v from the ign key. if you ground the wire for the light at the alternator plug the light should light up if the key is on.
 

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Do you have a volt-ohmmeter?

Nothing on, engine not running nominal battery voltage should be in the 12.6-13.2 range - that can vary a bit depending on battery age, length of storage and temperature.

With the engine running and assuming that this is not a one-wire alternator, you should see battery voltage at the alternator in the 13.5 - 14.3 - again it can vary a bit. IF it is a one-wire alternator, you normally need to raise the engine RPM to 2000+ which excites the voltage regulator and charges the battery. If you do not see this amount of voltage from the alternator - 98% odds the alternator is done.

An easy test with the engine running and you are seeing voltage is to turn on the headlights, heater, stereo - then on the volt-ohmmeter you should see a voltage drop, then recovery. This indicates that the battery encountered a voltage reduction from the operation of a component, the voltage regulator sensed it and adjusted the voltage to compensate. If you do not see a recovery, (in fact while watching your volt meter you should be observing the voltage dropping) then the voltage regulator is not working. On most of today's alternators, it is an easy part to replace and much cheaper than replacing the entire alternator.
 

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And be sure you've got the alternator wired correctly so it's getting excitation, which signals it to charge!
Of course if everything is correct, it's not unusual to find new alternators that are junk these days too.
 

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If this is a new install, then the wiring needs to checked to make sure it's correct for the alternator.
If you have a separate regulator, you can disconnect it and feed 12v to the armature wire to have it generate maximum output.
If you have an older GM (70s?) style with an internal regulator, there's a tab inside the alternator that you can ground to do the same.
Newer alternators with internal regulators likely have a functionally similar way to bypass the regulator.
If the alternator output picks up dramatically when bypassing the regulator, the regulator isn't operating properly.
If it doesn't, then the problem is likely in the alternator itself.
Internal regulators can be swapped out.
Brushes and bearings are the other most common problems with alternators, and both are easily replaced.
For any additional advice, providing alternator design details and/or model number would be helpful.
 

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Discussion Starter · #7 ·
So the wiring on this thing is a hack job. I was hoping to keep things going until I can set aside enough time to put in my wiring kit but that may not happen for a while. I'll grab some pics and try to explain at some point.
 

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Quite a few of us have engaged in some wiring hacker work ourselves over the years so if you post some photos, we may be able to fix you up temporarily.
 

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🐔County, TN. 55 Bel Air Sport Coupe
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And be sure you've got the alternator wired correctly so it's getting excitation, which signals it to charge!
Of course if everything is correct, it's not unusual to find new alternators that are junk these days too.
That's what the GEN light bulb does. And yes if it's burned out, it won't excite the alternator. Although I've heard of some 3 wire alternators that if you give them a little rev like some one wire starters need to charge, they will then start to charge without the voltage from the GEN light. I don't know that part personally, just read it here or on HotRodders or somewhere.
 

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That's what the GEN light bulb does. And yes if it's burned out, it won't excite the alternator. Although I've heard of some 3 wire alternators that if you give them a little rev like some one wire starters need to charge, they will then start to charge without the voltage from the GEN light. I don't know that part personally, just read it here or on HotRodders or somewhere.
On a stock vehicle the gen light does. But all my hotrods get volt meters, so no gen lights. The wiring systems I use come with a white wire marked "excite" that attaches to the correct alternator terminal.
 

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🐔County, TN. 55 Bel Air Sport Coupe
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On a stock vehicle the gen light does. But all my hotrods get volt meters, so no gen lights. The wiring systems I use come with a white wire marked "excite" that attaches to the correct alternator terminal.
I wasn't talking about your car!

The original poster mentioned a possible problem with his GEN light. He said it doesn't come on anymore.
 
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