Be carefull what you take a spur from! if you do as DIscomania suggests make sure you fit a low rated in line fuse to rpotect your CD player and your wiring loom/sparks etc...
To be honest if you can isolate the speaker wires, you should be left with 2 (a positive and an earth)
on on later Def's the switched live was green and the constant live was Red, earth (or in our case negative) was black!
I would suggest you go through it all with a multi meter and isolate one by one to be on the safe side.
PUT A FUSE IN FOR SAFETY'S SAKE. HOPE THIS HELPS AND GOOD LUCK