How to add a Meta Pass to a custom shader to Emit light using enlighten

Hi, I'm using custom cg shaders in my game and I want one of them to emit light. It should be baked into the lightmap.

A little research showed that this has to be done using a Meta pass, but how exactly that needs to look was nowhere to be found.

In the buildin Shaders zip file I found an example though, but that does not seem to be working.

here is the Meta pass I'm currently using, as found in the buildin_Shaders.zip ("Legacy Shaders/Self-Illumin/VertexLit")

     Pass
     {
     
         Name "META" 
         Tags { "LightMode" = "Meta" }
         Lighting on
         CGPROGRAM
         #pragma vertex vert
         #pragma fragment frag
         #include "UnityCG.cginc"
         #include "UnityMetaPass.cginc"
 
         struct v2f
         {
             float4 pos : SV_POSITION;
             float2 uvMain : TEXCOORD0;
             float2 uvIllum : TEXCOORD1;
         };
 
         float4 _MainTex_ST;
         float4 _Illum_ST;
 
         v2f vert (appdata_full v)
         {
             v2f o;
             o.pos = UnityMetaVertexPosition(v.vertex, v.texcoord1.xy, v.texcoord2.xy, unity_LightmapST, unity_DynamicLightmapST);
             o.uvMain = TRANSFORM_TEX(v.texcoord, _MainTex);
             o.uvIllum = TRANSFORM_TEX(v.texcoord, _Illum);
             return o;
         }
 
         sampler2D _MainTex;
         sampler2D _Illum;
         fixed4 _Color;
 
         half4 frag (v2f i) : SV_Target
         {
             UnityMetaInput metaIN;
             UNITY_INITIALIZE_OUTPUT(UnityMetaInput, metaIN);
 
             fixed4 tex = tex2D(_MainTex, i.uvMain);
             fixed4 c = tex * _Color;
             metaIN.Albedo = c.rgb;
             metaIN.Emission = c.rgb * tex2D(_Illum, i.uvIllum).a;
             return UnityMetaFragment(metaIN);
         }
         ENDCG
     }

The whole thing seems a little wonky anyway, sometime it works with the legacy self illu shader, sometimes it does not, or only after restarting. I don't know enough about how the system works to have an Idea what goes wrong here. does anyone have an idea how to get this working?

cheers Simon