Few things you need to do first:
Since your trikes stator is AC power, you cannot plug an HID system into the power. It will not light, only flicker. You need DC current to light an HID.
Step 1. Convert your stator to a floating ground. Basically all you have to do is lift the ground lug off of where it grounds to the engine, then solder a wire to this and run it out.
Step 2. Buy a TrailTech Voltage Regulator Rectifier. I got mine from RockyMountainMC.com for about $45 shipped to me. Then wire it in as per the instructions.
Step 3. Get a 12 volt 4AH lead acid battery. This will keep the voltage supply to the light constant so that it will not burn out and re-light on you when you get off and on the gas. Wire it as per the instructions with the voltage regulator/rectifier.
Step 4. Mount up your light, ballast and hide your wires.
I would probably run a 35 watt HID. It puts out around the same light as a 65w halogen bulb, but with half the current, plus your stator should handle it fine if it's a 50 watt.
This mod will also allow you to run LED's too
LED obsessed
2015 Yamaha FJ-09