Alternator Excitation Circuit

[Shern]

I've noticed a few of us seem to have the issue whereby our alternator's fail to generate until we blip the throttle.

I always assumed this was normal. It is not.
In most threads people are steered toward new alternators or regulators but I do not believe that is the issue.

The circuit seems to work as follows: three wires going into the alternator, two red 12v, one blue exciter wire. The exciter wire is part of a circuit between 12v and the idiot lights in the cluster. When the idiot lights are on, exciter wire serves as a ground, illuminating the cluster lights. When the alternator is generating, the exciter wire becomes 12v (positive) turning the lights off.

In theory, if the lights are coming on, 12v should be making its way to the alternator and exciting it, engine turns over, alternator makes power, fin.

In practice, this doesn't seem to be happening. Instead, by blipping the throttle, we are manually "bootstrapping" our alternators into generating.

I removed the alternator harness today and checked it with my multimeter.
I got battery voltage at the two 12v terminals, but only 11.7 volts at the exciter wire. I don't know enough about this stuff to know whether that's sufficient to excite the alternator though it would appear not. Current thinking is additional resistance is dropping that voltage.

Who has encountered this?



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