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Ignition Warning Light



Freshman Member
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I just installed an alternator. When I switch on the battery, the ignition warning light comes on. When I turn on the ignition, it goes off and stays off when I crank car. I thought it should come on when ignition is turned on and go off when engine cranks. Any ideas what is wrong?


Darth Vader
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Cappy, I will attach two pics of the way I wired my AC Delco, 3-wire alternator in my BJ7 Healey. It has been running this way for about 10 years now. Hope this helps. In the one pic it shows an Amp meter. Skip the amp meter as it will not record accurately as shown. But the #10 red wire must be connected from the main alternator Battery terminal to the solenoid terminal that feeds thru to the battery.


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Darth Vader
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Just a point of clarification about the charge indicator wiring with the 3 wire alternator. You will notice that the indicator light has 2 wires on it that both appear to be coming from a source of voltage. The light will be off when both those wires have the same voltage on them. In other words, when the alternator is not turning the light sees voltage from the ignition switch run terminal when the ignition switch is in the on position. That is battery voltage. But the other wire on the charge indicator light goes to the alternator. When the alternator is not turning and therefore not generating any voltage then this side of the indicator light sees ground thru the alternator and the light lights up. As it should when the key is on but engine not running.
When the alternator starts to turn and therefore generates voltage the both sides of the charge indicator light have the same voltage therefore no difference of potential across the bulb and the light will not light up. Therefore when the alternator is putting out voltage the light goes out because it has the same voltage on both sides of it. Also this arrangement provides an indication of when the alternator is not putting out enough voltage and starting to fail as this light will flicker or come on solid even when the engine is running. Hope this helps.


Freshman Member
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Just got back to my light problem. Thanks Darth Vader, for pointing out that two wires from a power source go to light. I found a bad connection on the small wire to alternator. When fixed it works as it should.
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