The lighting coil is a series of windings. The number of windings depends on which type you have. The wires for lighting are usually yellow or white. Takes the side cover off and look for damage. Make sure the windings are dry with no corrosion. You should be able to get a resistance measurement across the windings. I don't know about your year bike, but it would be something like .7 ohms white to ground or .6 ohms yellow to ground (wires disconnected from the regulator). No reading means an open circuit, but that is unlikely since you are getting some power to the headlight.
A dim headlight is usually the result of broken strands inside the wires to the headlight. This is from all the flexing as the bars turn back and forth. I would run a jumper wire from your regulator directly to the bulb thus bypassing all wires and switches. Do the same thing for the ground wire too. This is the first step before looking at the stator.