Quoted from Strummy:
What do the other 2 do?
They are part of the warming circuit, this allows a small amount of current to flow thru the bulb filament. Not enough current to light the the bulb, but enough to warm the filament. This makes the bulb light up quicker more light a flash. It also extends the bulb life. When installing led flash bulbs the warming circuit needs to be disconnected otherwise the the small amount of current will make them light all the time.