Most of them will fit a Chang with little adjustment to the holes for mounting. If necessary make the hole a bit bigger with file or drill. If the holes are too large use a big washer on each side.

Trust me this is not brain surgery. If you have the normal wire in the headlight Chang just take out the one screw that removes your headlight, unplug it and put it out of the way. This will expose the switch. Test to see what each wire does and disconnect the battery. Write it down if you are half way though a six pack. On most Changs there seem to be two to three wire on the ignition switch. Most switches are marked on back or in the direction with battery, ignition, and accessory. The clever folks who make them abbreviate them to batt, ign, and acc. Do we see a pattern here? So hook the wire from the battery (power from the loom that is always on) to batt, the one that goes to running with lights on to ign, and the one that runs with lights off to acc. Then it works like a Chang switch.

You could also use the starter one on the back for the starter if you wish to dispense with the separate switch. Changs tend to use two types of terminals. Spade type, and if you did not get a spade type switch you will have to change the terminal to bolt on or ring terminals on the wire ends, or ring terminals that are too small. I had the rings on this bike and drilled them out to fit.

The first picture shows installation of the wires, the second shows the switch installed, the third shows the switch mounted from the bottom, and the forth shows what the wires in a plastic Chang looks like so quit complaining.

Adjust the backing ring on the switch to fit your hole. It is going to be fairly thin on a Chang headlight. Test tighten the switch upper locking nut and if it fits remove and put it back with a drop of locktite. Connect the battery and try the switch.

If it works the way you wish reinstall the headlight and you are off.