Installing a basic alarm in the VW Jetta saves money on insurance and deters thieves looking for easy entry. Protecting the VW Jetta requires a working knowledge of car wiring and overall electrical systems. Alarms that are more complex can include remote start, motion detection and paging on capable alarm modules. Jetta models with power windows have different wiring than those without. Remove the panel under the steering wheel of the Jetta by opening the small panel on the left side. Remove the screws and pull the panel out of the car. Snap out the kick panel on the left driver’s side in front of the door. Pop the hood and remove the positive battery cable from the terminal. Mount the siren in an open area of the engine bay. Face the siren toward the engine to limit water exposure when driving. Connect the alarm power wire to the positive battery cable and combine it with the siren wires. Pull the wires along the firewall and into the wire bundle entry in front of the steering wheel.