The power technology in lamps and windshield wipers today are really quite sophisticated. It is under the control of the microcontroller, which tells it how much power to allow. Rather than just turn on, it says 'I know this load on this lamp to be 4A,' and if the load exceeds that value, the lamp will turn off immediately. A traditional relay control would just turn it on, despite the short, and would burn up. Then you would have to buy all kinds of expensive pieces instead of replacing a bulb or a small wire.