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Re: alternator leads Posted by Ari [Email] ![]() ![]() In Reply to: alternator leads, jeffb, Mon, 10 May 2004 11:57:50 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The B+ is a fat wire, usually red, that goes to the battery. That's the main current lead for power from the alternator.
The D+ is a thin wire, usually yellow or green. It runs up to the BATT light inside the dashboard.
The alternator uses electromagnets to make an electric field. These are called the field coils. The current to creat this magnetic field comes in through the D+. When you turn the key to ON, current flows from the key, through the BATT light, into the D+ post, and energizes the coils. Since current is flowing, the BATT light comes on.
Once the engine starts and the alternator is spinning, it starts to create its own voltage. The Voltage Regulator takes over, and supplies current into the D+ (internal to the alternator). Since no current is flowing through the BATT light bulb, it goes out.
If the wire to the D+ breaks, the alternator won't work. Even worse, you won't get a BATT light to tell you there is a problem. So inspect that wire every year or so - they like to corrode, and since they're thin, they can corrode to the breaking point.
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