i'll answer here so people know where it is
you've got the 2wd car so i'll assume you've got the early button locks rather than the later handle locks
the handle locks only have one cable which operates the central locking motor, whereas the button ones have 2 rods which run alongside the door skin
over time, the grease stops them from moving smoothly and this then tends to burn out the central locking motors
both front doors are "master" motors and will have 4 wires, one earth and then one to lock and one to unlock plus the trigger wire to feed everything else
the good news is that you can use the motors from the newer cars
the bad news is that they run the "other" way so when you would trigger them to lock, they would unlock and vice versa
ok, first step, remove both front door cars
some screws around the outside plus 2 underneath, don't undo the ones that are under the door pocket as these hold the door pocket in place rather than the door card
you will also need to undo the door handle as well as the little screw that holds the door handle cover plate in place
some people will also remove the wing mirror inner cover but you can wiggle them off without, but take it off just in case as you may need to do other stuff too later on if this won't work
it's easier to NOT remove the kick panels to unplug wires from there because they tend never to go back together again but if you knew what you were doing that would be the easiest thing to do, but more on that later if you need to do it
along the bottom of the inner door skin you will find several cable ties and several little clips holding the wiring loom inside the door in place, there will be several wires there, for the door open sensor, central locking, electric windows, electric mirrors etc but it's easier to remove all the clips and cable ties to you can figure out which one is which, the central locking should be a white plug but it's all bundled together so you may have to pick it all apart in any case
unplug both motors on both sides
once you've done this you can go on to "step 2"