If its the seat all the way in the back on the pilots side the seat belt is attached to the seat (i’m not sure if this is seat 7 or 8). In my 421 the right side is taken up by the beverage center and potty (which also has a seat and a belt).
Thank you. I called it the “8th”, since the potty is not really removable, but looking at other sites on-line, it is more correctly, the 7th seat. Yes, it is on the pilot side, sitting on the baggage shelf, next to the potty.