Tamron 1.4x on a Canon 100-400 question

I've two Tamron 1.4x tele-converters. One is the cheaper black AF, and the other is the white SP AF. When used on my 100-400 the cheaper black one will autofocus like a champ while the more expensive white one does not autofocus at all. I don't understand why since the pins look identical and was under the impression that the only difference between the two was the color and a little better optics in the white version. Any ideas about what I'm missing?

My black one only has 8 pins and I think the white one has 10 like the Canon.You may have to do the
tape the pins trick with the white one.Is the IQ much better with the white one?

halitime wrote in post #10026027
My black one only has 8 pins and I think the white one has 10 like the Canon.You may have to do the
tape the pins trick with the white one.Is the IQ much better with the white one?

Nope..they both have 8 pins and the mount looks exactly the same.