Look at the battery, if it has 3 cells, (caps where you check the electrolyte level) it's 6v, if it has 6, it's a 12v.
The lamps will be marked with their intended voltage.
If you find the lamp voltage to be correct, and they burned out, better check the alternator output with a volt meter. There could be a problem with the alternator or wiring causing it to overcharge. With a 12v system, the voltage should level off at about 13.5 to 14.5 volts at fast idle.