pulse switch? dc injector testing

130mikep

you'll have to forgive me im hopeless at electronics, i want to make a 12vdc circuit to switch a fuel injector on and off at a set frequency.
so i basically want a switch with an on, off and maybe a 50hz pulse setting or something?? i dont want to spend a massive amount of money(like a few £ tops!!), its only to see if i can replicate a fuel injector cycle so i can see the flow of the petrol through injectors outside of the car.

thanks, mike