That looks like an old fashioned headlight dip switch but I could be talking out a hole in my head, maybe it is a brake switch?
It is has 3 wires power in and one to dipped and then full beam...it fits in the hole next to gearbox tunnel for rhd or in the blanked off on the near side by A post operated by left foot...will upload pics of junctions on a 58 tomorrow just finished cleaning them up...@border