how to read in game objects in a list from different script

hey, i'm following a new tut for a RTS game. But there's only explained how to select each single object. So i fighted me through several tuts, and found a script attached to a unit prefab which detects if it's selected by drawing a rectangle for multi selection.
It basically works but i haven't found a way to read in those units in a List in a script which is attached to the maincam with witch the rectangle is drawn and there i declared the List.

This script is used with the main cam :

 public Texture aTexture;
 public static Rect selection = new Rect(0,0,0,0);
 private Vector2  _box_start_pos = Vector2.zero;
 private Vector2 _box_end_pos = Vector2.zero;
 public string Pl_tag = "Player"; 
 public List<GameObject> selectedObj = new List<GameObject>();
 
 void Update ()
 {
 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         RaycastHit hit; 
         Debug.DrawRay(ray.origin, ray.direction * 100.0f, Color.yellow);
 // Called while the user is holding the mouse down.
         if(Input.GetKey(KeyCode.Mouse0))
         {
             if (Physics.Raycast(ray, out hit ))
             {
                 //Debug.Log(hit.collider.tag  );
                 if(hit.collider.tag == Pl_tag)
                 {
                     var obj = hit.collider.gameObject;
 
                     if(selectedObj.Contains(obj) == false)
                     {
                         selectedObj.Add(obj);
                        
                     }
                     Debug.Log(Pl_tag +" hit");
                 }
             }
  else
             {
                 selectedObj.Clear();
                 Debug.Log("");
             }
 // Called on the first update where the user has pressed the mouse button.
             if (Input.GetKeyDown(KeyCode.Mouse0))
                 _box_start_pos = Input.mousePosition;
             else  // Else we must be in "drag" mode.
                 _box_end_pos = Input.mousePosition;    
         }
         else
         {
             // Handle the case where the player had been drawing a box but has now released.
             if(_box_end_pos != Vector2.zero && _box_start_pos != Vector2.zero)
                 //HandleUnitSelection();
 
             // Reset box positions.
             _box_end_pos = _box_start_pos = Vector2.zero;
         }
 /// <summary>
     /// Draws the selection rectangle if the user is holding the mouse down.
     /// </summary>
     void OnGUI()
     {
         // If we are in the middle of a selection draw the texture.
         if(_box_start_pos != Vector2.zero && _box_end_pos != Vector2.zero)
         {
             // Create a rectangle object out of the start and end position while transforming it
             // to the screen's cordinates.
             selection = new Rect(_box_start_pos.x, Screen.height - _box_start_pos.y,
                                   _box_end_pos.x - _box_start_pos.x,
                                    -1 * (_box_end_pos.y - _box_start_pos.y));
             // Draw the texture.
             GUI.DrawTexture(selection, aTexture);
         }
     }
  public static float InvertMouseY(float y)
         {
             return Screen.height - y;
         }  

This script is attached to the GameObject prefab called Unit:

    public GameObject  thistransform;
     public bool selected = false;
     private Renderer rend ;
    
 
     void Start()
     {
         Renderer rend = thistransform.GetComponent<Renderer>();
     }
     void Update () 
     {
        
         Renderer rend = thistransform.GetComponent<Renderer>();
         if(rend.isVisible && Input.GetMouseButtonUp(0))
         {
             Vector3 camPos = Camera.main.WorldToScreenPoint(transform.position);
             camPos.y = NewBehaviourScript.InvertMouseY(camPos.y);
             selected = NewBehaviourScript.selection.Contains(camPos, true);
         }
 
         if(selected)
         {
             rend.material.color = Color.red;  
         }
         else
             rend.material.color = Color.green;
        
     }  

So i would like to achiefe to read this game objects in the List selectedObj. If i understand it right selection.Contains(camPos, true) does return only Vector3 of each object ? I've tried very much but i'm out of any idea now.
I hope that all isn't to confusing the way i explained it here (i'm german)

so many thanks previously !!!