Swapping Ford RDS5000 for RDS6000?

Have a ford focus ghia 2001 with the old cassette RDS5000, managed to buy on ebay a silver RDS6000 that they said was compatible with the Focus. Tried swapping this over but the middle of the three plugs is half the size of the 5000. Can I buy the appropriate plug and swap this over, If so where are they sold, Want to get this sorted a.s.a.p as I'm already getting the dumb female jokes and that we shouldn't mess with gadgets especially electricals and CARS ..... if I get this sorted then I PROMISE NO MORE FROM HERE ON IN !!!!

Thanks

Jackie xx