If the player is more than a few years old I would replace it with a new one. We had an MR2 with 10 year old player and when you look at the advances in 10 years in electronics there is no comparison in terms of quality and features. You can get (UK) adapter leads and harnesses from Autoleads if the Sony was specific to that model of Celica - we had to with MR2. Standard manufacturers wiring and speakers are basic; if you get new CD player then think about upgrading speakers and wires - all depends on the value of the car though :-)