Wiring. Which way should power come in?

I have bought a modern after market start switch/engine on/ isolate switch for a 1978 Moto Guzzi I am building, and so the wire colours do not correspond to the wiring diagram.
As the starter is only momentarily making a connection when used, and the "engine on" switch remains as a circuit more or less at all times, my question is, does it matter which side of the switch that the power comes into?

NO it does not matter with the switch you have there.

That's what I thought, but wasn't sure, not being very au fait with electrics and their switches. I had wondered if the switch may be designed to flow power one way?

Thank you.