Circular Bar - problem with shader

Hi, I using AlphaCutoff shader to make my life bar circular. Its working half good - the texture disappears but it leaving black solid color behind it.
How can I change to draw _BackText instead of just solid black?

Shader:

Shader "Custom/LifeBar" {
    Properties {
      _MainTex ("Base (RGB) Transparency (A)", 2D) = "" {}
	  _BackTex ("Texture", 2D) = "black" {}
	  _Cutoff ("Alpha cutoff", Range (0, 1)) = 0.5
    }
    SubShader {
	Tags {"RenderType" = "Transparent" "Queue" = "Transparent" "IgnoreProjector" = "True"}

			 Pass{
		AlphaTest Greater [_Cutoff]
			Material {
				Diffuse (1,1,1,1)
				Ambient (1,1,1,1)
			}
			Lighting On
			SetTexture [_MainTex] { combine texture * primary }
		}
    } 
  }

Script to draw bar:

if (Event.current.type.Equals(EventType.Repaint))
        {
            mat.SetFloat("_Cutoff", lifePerc);
            Graphics.DrawTexture(new Rect((Screen.width - Screen.width / 6) - 5, (Screen.height - Screen.width / 6) - 5, Screen.width / 6, Screen.width / 6), gradient, mat);

        }

It hast to do with line 4, replace

_BackTex ("Texture", 2D) = "black" {}

with

_BackTex ("Texture", 2D) = "" {}

Add this to your shader:

Blend SrcAlpha OneMinusSrcAlpha

Provided that you’re trying to have the _MainTex be positioned on top of the _BackTex, this should work for you!

Shader "JM/LifeBar" {
//Jona Marklund 27th of August 2013

    Properties {
      _MainTex ("Base (RGB) Transparency (A)", 2D) = "" {}
      _BackTex ("Texture", 2D) = "black" {}
      _Cutoff ("Alpha cutoff", Range (0, 1)) = 0.5
    }
    SubShader {
    Tags {"RenderType" = "Transparent" "Queue" = "Transparent" "IgnoreProjector" = "True"}
 
          Pass{
       AlphaTest Greater [_Cutoff]
         Material {
          Diffuse (1,1,1,1)
          Ambient (1,1,1,1)
         }
         Lighting On
         SetTexture [_BackTex] { combine texture * primary }
		 SetTexture [_MainTex] { combine texture, previous + texture }
       }
    } 
  }

Best Regards
Jona