Central locking kits

Hi, I'm looking to get a central locking kit for my mk3 (mk2f). I don't want a 'remote' kit because I want to use my existing Cobra alarm to control it, which says it has 'Universal Central Locking Output' in the brochure. So my question is what is 'universal'? I've had a quick look and something about a negative earth signal (maybe wrong I don't know!) and a pulsed signal (again may be wrong!).

Also I don't want to burn out the actuators trying to lock the drivers door if it's open, because it can't be locked when open. Would my alarm not try to lock the doors if it knew the doors were open? I don't have much info about my alarm, its a Cobra 3998. I've found a picture of it online and there doesn't appear to be any unit other than the siren, does this sound right? The whole immobiliser unit is in the siren casing? That would explain why I can't find another box for it I suppose. If that is it then I guess I can try to find the c/l output and see what it does with a multimeter... anyone know what it looks like? How many pins?

So can anyone recommend a kit suitable for a mk3 (2f) polo? I don't want the boot being done, just the two front doors.

Thanks,

Ray