Texture2D Load only returns red channel

How did you define BackBufferMap? Please note that Load() gets texels without filtering and it uses integer offset, not UVs (pretty much raw access to memory).
Also you return only float, which is single number, wonder why that code even compiled for you.
If you're simply rendering fullscreen quad it's normally done like this:

SamplerState BackBufferSampler : register(s0);
Texture2D BackBufferMap : register(t0);

float4 PSDisabledMain(in float4 screenPos : SV_POSITION) : SV_TARGET0 {
    return BackBufferMap.Sample(BackBufferSampler, screenPos.xy);
}

I think that Zaoshi Kaba is on the right track here - you're returning a single float from your shader, whereas for colour you would normally return float4 instead; have you checked your shader compiler output for any warnings?

Also note the comment about using Load - this may seem fine for simpler effects, but if you're going to be doing anything that distorts or warps the texture, you will definitely be wanting a linear Sample instead.

I am totally confused right now when I use sample the screen is simply red, but the general problem persists.

Why is Load only returning the red value?

the color variable always just receives the red value and the rest are underscores in pix...

The shader with vertex shader

float4 VSMain(in float3 Position : POSITION) : SV_Position 
{ 
	return float4(Position, 1.0f); 
}

float PSDisabledMain(in float4 screenPos : SV_Position) : SV_Target0 
{ 
	//BackBufferMap.Sample(TexureSampler, screenPos.xy);
	int3 sampleIndices = int3(screenPos.xy, 0);
	float4 color = BackBufferMap.Load(sampleIndices);
	return color;
}

The vertices used:

glm::vec3 vertices[] =
{
	glm::vec3(-1.0f, -1.0f,  0.0f),
	glm::vec3(-1.0f,  1.0f,  0.0f),
	glm::vec3( 1.0f, -1.0f,  0.0f),
	glm::vec3( 1.0f,  1.0f,  0.0f),
};	

The vertices and Load function is simply the same I am using in my deferred rendering shaders...

And here's how I create the backbuffer:

	D3D11_TEXTURE2D_DESC backTextureDesc;
	D3D11_RENDER_TARGET_VIEW_DESC backTargetViewDesc;
	D3D11_SHADER_RESOURCE_VIEW_DESC backResourceViewDesc;


	ZeroMemory(&backTextureDesc, sizeof(backTextureDesc));
	backTextureDesc.Width = width;
	backTextureDesc.Height = height;
	backTextureDesc.MipLevels = 1;
	backTextureDesc.ArraySize = 1;
	backTextureDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
	backTextureDesc.SampleDesc.Count = 1;
	backTextureDesc.Usage = D3D11_USAGE_DEFAULT;
	backTextureDesc.BindFlags = D3D11_BIND_RENDER_TARGET | D3D11_BIND_SHADER_RESOURCE;
	backTextureDesc.CPUAccessFlags = 0;
	backTextureDesc.MiscFlags = 0;

	HR(m_d3dDevice->CreateTexture2D(&backTextureDesc, NULL, &m_BackTargetTexture));
	
	backTargetViewDesc.Format = backTextureDesc.Format;
	backTargetViewDesc.ViewDimension = D3D11_RTV_DIMENSION_TEXTURE2D;
	backTargetViewDesc.Texture2D.MipSlice = 0;

	HR(m_d3dDevice->CreateRenderTargetView(m_BackTargetTexture, &backTargetViewDesc, &m_BackTargetView));

	backResourceViewDesc.Format = backTextureDesc.Format;
	backResourceViewDesc.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE2D;
	backResourceViewDesc.Texture2D.MostDetailedMip = 0;
	backResourceViewDesc.Texture2D.MipLevels = 1;

	HR(m_d3dDevice->CreateShaderResourceView(m_BackTargetTexture, &backResourceViewDesc, &m_BackResourceView));

See this:

float PSDisabledMain

It means that your pixel shader is just returning a single float. Change that "float" to "float4".

Oh god can't believe I didn't notice that! Thank you so much!