Normally an aftermarket cd player in the Ka uses an adapter to convert the ford aerial connector to a conventional one. Check the end of the connection to make sure part of it doesn't detach. (check ebay for some pictures of these)
If part of it doesn't detach then the person who fitted it may have changed the plug by cutting it off and rewiring a new plug, or by rewiring right the way through the car to the aerial... Which wouldn't be the cleverest thing they've ever done in their lives!
Dave
February 2008