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"My voltage still drops when I start the car from over twelve with the car off to just under twelve with the car on."
Hi James,
Do you get the panel warning lights when the key is ON, engine off? If not, the alternator probably won't put out, and you'll be running off the (dying) battery. Four of those Warning lights are connected to the alternator D+ terminal via a thinnish red wire, which does two things:
1- Makes a ground path for the Batt light (and the others below*, via diode connections) TO and thru the alternator to ground. [The bulbs have +12V hard-wired to the other side side.]
The bulb current flowing thru the alternator causes it to produce voltage as it spins up. This is sometimes called "exciter" current, or more crudely, alternator foreplay.
2- Once the Alternator is putting out voltage, the wire also carries that voltage back to the bulb circuit to turn the lights OFF, . The D+ terminal (that was at ground level) should rise to Alternator B+ output level. So with voltage now on both sides of those bulbs, no current flows and they go out.
* The other bulbs whose current adds to that of the Batt light are:
• Parking Brake
• Brake Warning
• Bulb Failure
If this doesn't help, I suggest starting a new thread on the subject, or do a Search on it.
Bruce
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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