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Can someone explain the alternator/charge indicator circuit to me ?

3144 Views 4 Replies 3 Participants Last post by  cowboyup151
I'm looking at a schematic in a Haynes Superduty manual.

The "Generator" has 3 wires coming out of it: B, A and "-". Additionally, the alternator is grounded.

So... B goes to the batteries. Makes sense. This is the big cable connection.

A goes to the battery junction box and has a 6A fuse.

"-" goes to the battery junction box but has the key and charge indicator in the circuit.

I don't understand the function of A and "-".

One more thing: I thought the ECM controlled the field in these alternators and I don't see a field connection anywhere.

Thanks in advance to anyone who can explain this to me.
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Thanks for the reply.

So is the "I" or "-" circuit the field current supply ?

The thing I don't understand from all this is how come they put the "charging indicator" in that circuit. Shouldn't the charging indicator be in the "B" circuit, because that is where the current flows to the batteries ? Couldn't there be a situation where we feed the alternator field current and yet no current comes out to the batteries, maybe blown diodes or something ? I don't get it. If you understand their rational here, I'd love to hear it.

That I circuit is protected by a 5A fuse. The only thing I can think of is that the "-" output is charging voltage and the charge indicator is really showing the voltage difference between the alternator output and the battery voltage. When one turns on the key the "charge indicator" gauge gets connected between the alternator output and the battery and thus displays the voltage difference. Does that make sense ? It is then a "charging voltage indicator", not a "charge current indicator".

Guess what ? That symbol isn't an "-", it is an "I". The markings are turned 90 degrees on the generator symbol. I just noticed it.

I get it now.
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