Join Date: Sep 2001
Location: Temple City, Ca
<BLOCKQUOTE>quote:</font><HR>Originally posted by drew69:
John, BF was asking about the brown wire at the voltage regulator plug. From the diagram I looked at this is the correct answer.
You are correct. It does go where you have indicated. But why does it go there, what does it do, and is it needed on a one-wire?
Staying with the simpler GEN light circuit: From there the other side of the lamp goes to the ignition switch. Until the mid 70s, GM also used an additional resistor wire from the switch. About 10 ohms. This was in case the idiot light burnt out.
The purpose of running the circuit this way was not to power an idiot light, even though it does. An externally regulated alternator (or generator if you want), an SI, or a CS alternator requires a voltage to start. The field first needs to be excited or energized to begin to start producing. The field acts like like an electo-magnetic and needs voltage. If the car was just shut off the is enough residue flux in the field windings for it to start again. If it sits for a long time, this bleeds off. Once the alternator starts producing there is an output out of the field wire (blue) but first the alternator needs to start.
Without the 12 volts from the battery, through the ignition switch, through the idiot light, and down the brown wire, the alternator may not start again. Spinning a rotor inside an unenergized field (or stator) produces no output.
A true aftermarket one-wire alternator, an alternator with only the large red B+ wire on it, works differently. It does not need the external battery voltage to start or excite its field. It self excites itself when you get it above a certain RPM.