OK so I have done a bit more research and think I was close but also need to run a wire from -12v GND on the laser back to GND on my BOB..... here is a basic sketch as I think it needs to be... is this right??
Basically I'm concerned about connecting -12v to the GND on my BOB because everything else on it is -5V but I heard that a common GND is fine regardless and it's ok to mix-12v and -5v.