My friend recently acquired an early V6 converted MK3.
The ignition barrel immobiliser ring is behind the passenger seat, with the (V6) ECU and an old key taped to it! Presumably the key is paired to the immobiliser.
There is only 1 (black) key with the car, it starts the engine & the remote unlocks the car.
If we buy a replacement key, and try to pair it ourselves, would the immobiliser & other key taped to it cause an issue?
What we want to achieve: a spare key with remote button functionality. No immobiliser reprogramming. - can a new key be copied from the working one?
I'm guessing the key you use to start and lock/unlock the car with has nothing to do with the immobiliser. In which case, there's no need to pair it as the key taped to the immobiliser ring is doing that job instead.
EDIT: Scratch that. What car donated the engine? Have they used the ignition barrel from it? Do the keys look the same, that is, would they both fit ignition barrel and door locks? Then you'd be pairing it.