If your harness has a transponder key immobiliser, do not consider using it use it to immobilise your VW (by removing the key (or transponder) when you leave the vehicle) unless you either have a spare key / transponder chip, or are certain that you have enough info to allow a dealer to code a new key to your ECU if you lose the original key. The minimum information you would need to get a new key coded in the UK is either the VIN and registration number of the donor Subaru, or the immobiliser code as supplier on metal key ring tags when the Subaru was new:
If you don’t have the tag, the dealers use the VIN number and the registration to retrieve the code froma database. This may be different in other countries. If you lose the only key without this information, you will need a new set of immobiliser components (ECU, immobiliser ECU and transponder) for your engine before it will start again.
Also DO NOT extend the wire between the antenna and the immobiliser ECU. Doing so is likely to reduce the reliability of the system, or to stop it working all together with the MY00 - MY07 cryptographic immobilisers, and may also do so with the MY96 - MY99 fixed code ones too.