upgrading to a cd player

[gbfish]

i have just bought a second hand cd player for my escort. it is a standard ford unit so i thought i would just be able to remove the cassette player and connect the cd player and it would work. however, the radio works fine as do all functions but the cd player, i thought there must be something wrong with the head unit but my dad has just done the same thing in his scenic and has the same problem. is there something we need to do before cds will play?

[ugly_bob]

sounds like 2 dud units to me.
If the radio is working fine and coming out of the speakers, the unit is getting power and the output is ok.