There must be a reason why you require a "special" harness (atleast I think you require one). I have all the wiring info at home for my system. I'll check tonight to see what was wired differently for my BOSE system. You could probably get a better answer by asking PAC what the difference between the 21 and 21B is. It should be fairly easy to rewire the harness. Atleast it can't hurt to inquire.