Alpha channel not passing through

I’m testing different methods for blending channels together and I ran into an issue where I’m using a vector 4 parameter as a “channel mixer”. I’m appending the alpha color with the RGB then multiplying it by an albedo texture with a packed alpha, but the result is black when setting the alpha to 1. Regardless of any value I use in the alpha channel, it remains black. This should be similar to using a channel mask parameter, but it’s not working… ??