new cd player in corsa b not working

[ALfooy]

i've just brought a new sony CD for my corsa b, i've installed it correctly and there is power coming to the cd playrr as you can put a cd in and eject it no problem, but the display won't come and it won't actally play anything.

the power cable i've got has a male and female plug, but the old cassette player has three plugs with the third slightly bigger, one what does this do and two do i need a connector with three plugs.

any help would be grateful, cheers.