How do I power a car horn?

[aNewGuy]

I purchased a pair of car horns from sparkfun (https://www.sparkfun.com/products/10966?)
The potiential power draw has me a little concerned.
Rated Voltage: 12V
Rated Current: 8A

1)Do I have to provide that much power, or will it function quieter after some "on" threshold is met?
2)Assuming the whole 96 watts isn't required could I power one of these off a small wall wart (300ma)? What happens when a potientially large load is attached to a small supply? Will the supply only provide its rated maximum? If not could I limit the current with a suitably large resistor?
3) Do I need to worry about running this through a standard breadboard or regular hookup wire given the wattage?

Thanks, sorry if these are newbie questions.

 

[CocaCola]

In general car horns require a substantial amount of power... It's the poor mans battery check, if the horn works the battery is AOK if the horn sounds sick or doesn't work the battery is dead...

I'm guessing you will need several amps before they start to make noise... And I'm guessing the 300mA wall wart will puke it's guts before anything really happens...