Kirbby is right. The two wire switch is a simple on-off, and the new one is a high-low switch. If you want to have a true high-low function, the best way is to split the red power wire so that there is a place to hook up the brown wire from your new switch to it. The white wire from the switch (low beam) will go to the white from the headlight, and the blue (high beam) from the switch to blue of the headlight. You will then need to take the green wire from the headlight and hook it to the green wire from the wire harness. The soft tail Z50's had a unique set-up where the headlight has only wire going to it, and the wire that would usually be hooked to a ground runs to the tail light first and then a ground, allowing the tail light to be controlled by the headlight switch too. If you just want to hook the switch and have it work like original without high-low switching, you may need to change the blue wire connector on the headlight to one two wires can hook into if it is not already that way. Hook the brown wire from the new switch to the red wire, the blue from the switch to the headlight blue, and the brown and red wire from the harness hooked to the blue ones. You will want to cover the white terminal from the switch with some electrical tape to keep the possibility of shorting out the light when slipping it past the "low" setting. I have wired a '74 and a '76 softail in the last 30 days, with one wired as described above, and one wired stock.
