He's going the opposite way, from a 6 pin up to 7 for the trailer. Different than stepping down from 7 to 4 or 6. You can't manufacture a signal for a pin that isn't there. [lol] The good news is that the extra pin on a 7 pin is an AUX (auxiliary), usually for either battery charging or back up lights on the trailer and not strictly necessary.
I don't recall ever seeing any adapter that goes from 6 pins UP to 7 pins, most likely because of the technical reason I noted above. I would recommend that you change the truck end to a standard 7 pin and use a 7--> 6 pin reducing adapter if you ever need to tow something with a 6 pin connector.
