I just bought a trials bike and fitting one of these was the first thing I did.
Not sure if the wiring had already been cut/altered with bullet connections on my bike, but basically I snipped the eye off the brown wire off the new switch and crimped a new female bullet type onto the end of it (red ones from maplin £2 for 10) - that was purely as the existing wiring, one was female and one was male. Then my original kill switch was connected behind the plastic and just a case of unplugging the old and plugging in the new.
I don't believe it matters which way the wires goes round due to the way the kill switches work.