The front brake switch is operated by the hydraulic pressure in the brake line. If you follow the brake line from the master cylinder down toward the brake caliper, you'll find that it goes to a junction block bolted to the bottom triple clamp. The upper brake hose (from the master cylinder), the lower brake hose (to the caliper), and the brake switch are all attached to this junction block. Once you find the block, the switch itself is pretty obvious (it's the only thing that isn't a brake hose).
Before you start mucking with wires, check one easy thing first: pump the front brake up 5 or 6 times and then give it a real hard squeeze. Did the brake light come on? Since the switch works on hydraulic pressure, you have to be sure there is sufficient pressure to trip it. If your brakes are spongy, a light squeeze on the lever may not be enough (this is the voice of experience talking). If that's the case, you may need to service the front brakes.
If that doesn't do it, you'll have to start troubleshooting the wiring. The switch should have two wires coming off of it and going into the headlight bucket. Make sure those wires are firmly attached to the switch. If they are, you need to make sure the wires inside the headlight bucket are connected to the rest of the harness. You'll have to remove the headlight bulb and identify the wires from the switch and make sure they are firmly connected to the harness.
If all of that checks out, it's probably the switch itself. If you have a multimeter (for measuring voltage, resistance, etc.) you can check the switch by unplugging the wires from it and connecting the leads from the multimeter. When the lever is pulled all the way in, the meter should show battery voltage, 12 volts or so.
Welcome to the forum and let us know how it goes,
~john
