Just got done with that job. On mine it turned out to be the ground. You say one light is briter than the other ?? With a ohm meter look at the ground to the light fixture base on both sides. Should be a 0 ohms. Another way to test without a meter is to touch a wire from the base of each fixture to a ground on the engine, if it works properly with the wires just touching the base of each fixture, you got a ground problem. You see more of this in tractors than cars, you are always in the dirt. Turned out the joints between the pannels on the fenders had lost their ground. If this doesn't work, then you have a wire, switch, or fuse problem. Note here that I have a VN recon. I've noticed that there are many joints in the wireing harness that are just wraped together with tape over the joint. Over time I've gone through and soldered every joint or added a butt splice. Made the whole setup more reliable. I'm another one that took the turn signals and jumpered the wires together, turned them into flashers, don't think there is a need for turn sig in the U.S.
Chris