Best luck would be to get the timed relays from a car that comes with them. If you want to use a capacitor... you'd need a very large one, and also you'd need to do some math. You have to use the right resistor inline to make it discharge at the rate that you need... like a 1 farad car audio capacitor for example... at full charge if you took a wrench and touched both terminals... it would discharge INSTANTLY and you would have a new wrench/cap combo, because it would literally weld the wrench onto the terminals... so what you would have to do is buy some resistors... the problem is.. you need high watt resistors, which are harder to get. The small ones you always see at radio shack are 1/4 watt, lol, which is NOWHERE near what you need to run headlights. Good luck one way or another man, it'll be a fun project.