Central locking in a Celica, is a piece of cake. Buy the kit, Jaycar, Stratho's, Autobarn. 4 door kits are about $30.00. Have a look at what comes with it, and locate the solenoid just below the door latch. You will probably only use a couple of inches of the supplied rods.
Do not do what I saw in a TA22, the clown fitted the solenoid near the door lock button, then tried to fit the door trim over it!!!!