What does the brown wire in the alt plug do?

[readyman]

Not my choice, but I'm trying to work with it.
I'm trying to sort out a 12volt conversion. There is an OEM air conditioner on the driver side instead of an alt. So I'm working with the passenger side alt only.
I got a non-isolated ground alt for the pasenger side and just wondered what the brown wire in the alt plug(red/brown wire) is for.
The new alt is working fine but needs a ground attached to the block, I believe.
But the brown wire's job stumps me, should I leave it in after ground the alt to the block?

 

[doghead]

Single brown wire? Tach wire, You don't need it.

 

[readyman]

doghead,
no, the one in the white plug. It plugs in the back of the alt, passenger side alt. There's a red wire and a brown wire.

 

[readyman]

I checked the wiring diagrams and it goes to an alt relay. And the way the voltage changes when the key is 'on' just wondered what it did. Went to the Roscomm instructions and they don't mess with it in a 12v conversion. They just add a ground wire to the block.

 

[Warthog]

The brown wire in the red/brown plug turns on the excitor system in the altermnator.

The red wire provides constant voltage. The bown only provides voltage when the key is on.

It is required unless you have a single wire alternator (self exciting)

 

[readyman]

Thanks Warthog,
That's exactly what I wanted to know!
Now the wiring diagram and the alt2 relay make sense.

The brown wire in the red/brown plug turns on the excitor system in the altermnator.

The red wire provides constant voltage. The bown only provides voltage when the key is on.

It is required unless you have a single wire alternator (self exciting)