How do I render two scenes on top of eachother in THREEJS

Question

Please show me some code example on how to properly set the effect composer using threeJS to render two scenes on top of each other. I honestly don't understand why the second one is always clearing the first. I am using autoclear = false in the renderer.

I tried this

    `this.composer = new EffectComposer( this.ref );
    const backgroundPass = new RenderPass( this.back, this.camera );
    backgroundPass.clear = false;
    backgroundPass.clearDepth = false;
    backgroundPass.clearAlpha = false;

    this.composer.addPass( backgroundPass );
    
    const mainPass = new RenderPass( this.scene, this.camera );
    mainPass.clear = false
    mainPass.clearDepth = false
    mainPass.clearAlpha = false
    this.composer.addPass( mainPass );`