Using a DP3T Toggle On-On-On to switch between two devices and then have them both on
According to the switch drawing..which took forever to find..



Jumper:

Pin 3 to Pin 5. (Note 5 on Drawing)


Use:

Pin 3 : To Dynamo
Pin 4 : To Light,
Pin 2 : To rectifier/regulator , 


Though you could switch the latter two.

Switch function will be

Left - Rectifier
Centre - Both
Right - Light