Hi Rick,
Probably, there is that text in your radio screen now:
CODE----, this is coming after that when you have been taken off the radio from your battery and the radio is taken back again. Now you can put the 4 digits in but there might be a security system on it. If you have been tried to put the digits in 3 times then the next text is coming on your radio screen: CODE wait. It means that you need to wait at least 1 hour (the radio should be turn on) until you get the same text again: CODE----. Then you can put your code in.
Hope, this will help you.
Best regards.
Adam, February 2008