PJ2 and CV880
"The pushbotton itself is also a light - the button illuminates when activated, (held in magnetically); when it pops out, the light extinguishes"
"the blue light indicated start valve open and the buttons were pushed to start and originally latched in and released automatically at 35% N2"
That is the answer I was looking for.
Thankyou very much everyone for clearing this up for me.