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Discussion Starter · #1 ·
I've read most of the posts on this topic, but can't seem to figure out my problem. I have a 77 El Camino, with the internally regulated alternator. The Gen light comes on sometimes, just dimly. Checked voltages throughout the system. Battery voltage is 12.5 and brn alternator wire shows zero with key off, engine off. With engine running, the battery voltage goes to 14-14.5 and the brn alternator wire stays at 12-12.5. I checked from battery positive to the brn alternator wire with the engine running and get about 2 volts. I assume this voltage is what's giving me the dim red light.
What can cause the voltage to be different at the brn alternator wire versus the battery positive? Is this just a partially discharged battery?
 

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The brown wire needs to stay closer to the battery voltage with the engine running. What's happening is one side of the light is getting battery voltage through the ignition switch (14.5). The brown wire, the other side of the light, is dropping down to 12 volts. The 2 volt difference makes the light come on dimly. Getting close to rebuilding or replacing the alternator.
 

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If one of the three diodes in the diode trio is bad it will cause the light to glow dimly but the alt will still charge.
 

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Discussion Starter · #5 ·
Bang on. I took the alternator apart this morning and in fact found the diode trio was bad - one diode. Thanks for the good advice.
 
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