[csd]

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.

 

[klhansen]

Here's the blurb from the factory service manual

With voltage applied to I circuit, regulator is activated, allowing current to flow from B+ circuit to generator field coil. Generator generates an AC output which is converted to a DC output by a rectifier assembly internal to generatro, and is supplied to vehicle through the B+ terminal.

From the wiring diagram, the A circuit is always hot, and is switched by the I circuit (probably the one labeled "-" on your diagram) thru the ignition switch. There's a little box inside the generator labeled "Sensing and Switching Circuits". It's like a relay, with the A circuit doing the work.


PCM (ECM) only controls the second alternator in a dual alt setup.

Hope that helps

 

[csd]

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.

 

[klhansen]

You have it indeed.

The charge indicator light is in parallel with a resistor in the "I" circuit, and when battery and alternator voltage are the same, there's no voltage across the light. When there's a problem, there's voltage across the light and it lights up to indicate a problem. The resistor is there to let enough current thru to turn on the relay so the "A" circuit can energize the field.

 

[cowboyup151]

I have dual alternator I just had both rebuilt. But now i'm getting a control fault code for the lower alt its a 1106, does any body had this problem? Its charging fine on either alternator when isolated ? I've gone thru the troubleshooting steps from ford maintenance manual for the code but don't see any problems. But the code comes back.