This isn't a radio that I'm familar with, I'm afraid.
However, there appears to be quite a lot of useful infomation about it and it's codes here:
instant-radio-code.com/delphi-ford-b420-low-radio-...e
Your Ford Ka is really just a Fiat 500 in disguise, it was actually built in a Fiat factory - that's why it has a Fiat audio unit in it.
Did you have any luck with your radio.
We have got a similar problem with a car we've just bought.
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