KCA-121B For Alpine

http://www.crutchfield.com/S-zbqDD4Puslq/cgi-bin/ProdView.asp?i=500KCA121B&search=KCA%2D121B

My cd player says i can use this, BUT the plug on the bottom of my cd player looks rectangular, not circle like all the pics i can find on sites that sell these.

Anyone know what i need to do? Thanks