Perhaps you can start by checking the fuses, the generator, voltage regulator and the light switch.
If the fuses are OK then I'd check or replace the voltage regulator next since the generator would more likely wear out than just stop. The voltage regulator has kind of points in it that close when the battery needs to be charged and the current is allowed from the generator.
It seems that the problem with the lights is separate, but the switch might have shorted out when the battery was in wrong.