VERY easy if the wiring is there (I've got a mk1 S and it didn't have jack), but if you haven't you can still pretty much work it out if you go to a breakers yard and get the right multiplugs from doors and wiring harness etc (got mine for a tenner, although I removed it myself and it took me three hours
), if they'd got it out it would be £50
the universal ones are dodgy, VERY slow and often screw up, my mate has one on his ford ka (a joke in itself, I will never work on it again, just a joke piece of junk manufacterd for way less than that of a punto yet they cost more?) and it often takes a few attempts for it to actually close, in which time it can overheat and give up totally, absolute useless. its actually quicker to turn car off, pop bonnet, disconnect battery, close bonnet, close doors manually then go than it is to use the universal thing
for a mk1 (or ~ish) you need:-
-central locking motor for each of your doors (either 2 or 4), here I found I didn't need the entire lockmechanism, JUST the white plastic bit that clips in -
underneath to the normal manual lock.
-door wiring for each of the doors
-cabin wiring that matchs up with each of the doors (2 door is very simple here, as 4door requires you to pull the b pillar plastic and carpet and sill covers etc etc, very fidely and tedious work, esp when its hot
-auxiliary fuse box (not sure if mk2's have them or just a different normal fusebox)
-wiring to fuse box, you can take part of the loom (if you follow the correct colours etc), or the whole thing and do a complete rewire.
-central locking computer, on a mk2 AFAIK its part of the dashcomputer (got another name though), but on a mk1 its a little black box at opposite end of car to the fusebox? with a little flashy light!
If your coming to stanford I'll show and explain it all to you using my car as a demo (did it like 4weeks ago, and took me 3days to strip scrap car of goodies, then strip my car, and rebuild it all with goodies!)
add to that, if the scrap car doesn't have the original key, don't worry, I'm pretty sure that META do a yellow relay and blippers for mk2 aswell! if not I'm sure there will be some way of bodging it all up, again, if coming to stanford I'll check it out for you!