OK, no lights. Start with the easy stuff. cranetruck has posted so much on the electric system just checking out his many posts will give you an education. Grounds are where you begin.
Get an ohm meter, turn the light switch on, and see if you have power in the light wires. You can disconnect the wiring at the light, insert the probe to the wire and get a good ground. If you have power there, then the light ground needs cleaning. This can be done with all the lights including the brake light.
I made an extra long clip wire for my ohm meter. About fifteen feet. So, I can test a circuit from the start to the finish with the ohm meter. I keep working toward the beginning to find where the problem is located.
It is possible you have bad bulbs or a short some where in the wiring. Once all that is checked you can check the light switch the same way. If the light switch is good, then you are not getting power to it.
On my second deuce I found the wiring was wrong at the rear. Turning on the running lights lit the BO lights and vice versa. I have no idea how long it had been that way but I had to make two short wire extensions to solve the problem.
