Car headlights is actually a fairly easy load to hook up to power supplies. Because the resistance of the filaments is a lot lower when they are cold there is a big inrush. For example a 12V 100W light won't just draw 8.3A at switch on. It's probably more like 40A until the filament is hot. Hooking up a 12V light to a 5V supply will provide fairly significant load.