Alternator wires

[Guest]

I am fitting an alternator to a diesel engine that has not had one before. There are three wires coming out of the alternator one thick red, one thick black and a thin brown one.Can anyone tell me what they connect to. I have a battery in place waiting to be charged and a starter motor bolted on

 

[andyball]

Mmmmm...red +'ve, black -'ve, brown....probably to a charge warning lamp.

Try to find out what alternator it is and chat up a local auto-electrician.

Otherwise....the above may work. IF it's a built in regulator type alternator.

 

[Guest]

Sounds like you need to connect the brown wire through the filament of the warning globe, to positive from the ignition switch, to enable excitation of the rotor. When running, 12v is developed on the brown wire (if chargeing) which turns the warning light off as 12v is present on both sides of the globe.
Make sure the pulley on the alternator is a 'one piece' one, not 2 halves spot welded together. they tend to split apart with the torque of a deisel engine.

 

[colinroybarrett]

John,

Can you find out how old, and where the alternator came from? If less than twenty years old, and off of a smallish vehicle, it almost certainly is machine-sensed, the regulator being built-in to the rear of the unit. Look for a small plastic housing, part of, or near to the brushes, where the brown wire exits.

If so, the brown wire goes to one side of a 2.2watt 12-volt bulb, the other side of which goes to your ignition switch, or to battery +ve via a new switch, if you’ve no ignition key, as others here have suggested.

If the alternator is a bigger commercial unit, it may possibly need an external regulator. Try looking at the wiring diagram for the vehicle it came from?

With only three wires, this sounds unlikely though.

 

[Guest]

Thanks for your suggestions, but do I take it that the red is obviously positive and goes to battery terminal and then black to the negative terminal? The alternator is a recently reconditioned unit