if its aftermarket, find the brain, follow the wires from it and chop out where they connect to your loom. join together any wires that have been cut into matching wire colours. if its factory, should find 2 pin plugs which can be removed then you find late spec mk3 without alarm, nick the 2 pin plug joiners and fit to your loom to rejoin. 2 that come to mind are yel/blue for fuel pump relay trigger and red/black for starter.