why starter have 2 wires?

Having replaced all the cables in my car, let me try to pass on what I learned (which is not a whole lot):

There is one positive cable that goes from the battery to the starter.  Then from the starter, there's a positive cable that goes to the alternator.  There is also a "trigger" or "exciter" wire that goes to the starter's solenoid from the ignition area (perhaps from the ignition switch?).

I hope that answers your question.  If not, I'll be quiet now.

The 2nd start is for more fuel during crank, no?

Instead of pulseing the injectors, it sends "fullblast", as determined by the computer.

 I worked overhauling starter motors for over 20 years.But I have not touched one in the last five years.I have lost touch a bit with things but this info may help explain the extra wire.

The  first wire that is connected from the ignition brings in the solenoid to energise the starter motor.

The second wire sends out a feed when the starter is engaged.

The reason for this is that the battery voltage will drop from 12v to 9v ( approx ) when the starter is turning.

Older type ignition systems used an ignition coil with a resistor .This coil opperated at 9 volts under normal running.

When the starter was ingaged the second wire would feed the coil, bi- passing the resistor.This kept the coil voltage constant under cranking power.

I am sure this theory applies to what ever system you have.In short it does not allow the voltage drop to effect what ever circuit is being feed,to give you better starting.

Phil

If im off the mark, disregard... But it seems to me that he wants to know why there are two starter wires at the ignition switch.  It thats the case, I will try to explain.  For example (2000+ nissan).  They have two starter wires coming from the igniton switch.  One is a normal starter wire, which goes to the starter relay. 

Other than that, it would be useless to have two starter wires.  It does not "crank" the starter.  It is a low amp circuit with a relay.  (usually)!!

Hak