Simple Blinking when mouse click script help

this script works, when play, the sphere will start blinking. which is not what i wanted. i wanted it to blink when i Input.GetMouseButtonDown(0). i try to put the sphere_blink(); inside Input.GetMouseButtonDown(0). But it will on when first click and off 2nd click. which also wrong. what i wanted is when i Click, then the sphere start Blinking. some1 please help me check where should i change in my script. Thx

private var hitPos : Vector3 ;

private var hitObjectPos : Vector3 ;

private var hit : RaycastHit ;

private var Down : boolean = false;

private var blip : GameObject ; //<--sphere11

var timer : double ;

var onoff : boolean;

 function Start(){

  blip = GameObject.Find("Sphere11") ;

  blip.renderer.enabled = false ;

}

 function Update(){



   sphere_blink(); 

   if(Input.GetMouseButtonDown(0)){

   Down = Input.GetMouseButtonDown(0);

   var ray : Ray = Camera.main.ScreenPointToRay(Input.mousePosition) ;

   

   blip.renderer.enabled = true ;



   if(Physics.Raycast(ray , hit)){

      hitPos = hit.point ;

      hitObjectPos = hit.transform.position ;

   }

}

}

 function FixedUpdate(){

    blip.transform.position = Vector3(hitPos.x , 5 , hitPos.z) ;

}

 function OnGUI(){

   //The world position of the ray's contact point->

    if(Down == true){

       GUI.Label(Rect(5,50,200,50),hitPos+ "") ;

    }

}

 function sphere_blink()
 {

  if (Time.time > timer)

  {



      timer = Time.time + .4;

      onoff = !onoff;

      blip.renderer.enabled = onoff;



   }

}