I own a 1965 bug. My windshield wipers, horn and all lights on one side in the back do not work.

Some of the fuses were the wrong amperage and had been blown. I replaced them. Also cleaned the light assembly and made sure it was getting good contact. Are these electrical things possibly related? What would be my next step in troubleshooting?

The ground to the frame for the lights that don't work. Probably corroded.

If ground is intact, follow wiring from lights to harness from lights, visually check what wiring you can, see if you can determine if circuit trips when horn is applied, light turned on, when brakes applied, when reverse is engaged, start with all loads off.
How are the fuse holders, verify voltage on fuse holder, and not so much the fuse.