okay...

the switch has 3 circuits... one goes to the battery.... one goes to the ground.... one goes to what you're wiring...

there should be a sticker on the side of the switch telling you what circuit is what....

wire the ground, make sure it is wired TIGHT... your ground needs as much contact as possible... then put the other end into the SWITCH not what you're wiring....

then wire whatever it is to the switch....

then wire the switch to the battery... again... as much contact as possible... should be good!