Everything on the left side of the circuit diagram is already in your car. The two components on the right side are all you have to add, just a relay, and a capacitor.
Read the previous post again, and notice that just not any 12V relay will work. You will have to go looking for one that has a higher coil resistance compared to "automotive" relays such as made by Bosch.
The capacitor value controls the duration of how long the relay is pulled in, the bigger, the longer...
Basically, the current through the relay pulls it in as the capacitor charges when you turn on the ignition switch. When you turn the switch off, the relay discharges the capacitor backwards into the car. The current pulse/duration through the relay coil is similar in both directions, except for the direction.