I have a two lamp f15 fluorescent fitting. Originally, I wanted it to have staters, but then I realised that I really need a two lamp manual preheat. the fixture switch is on the cord, so I don´t need one but I need a diagram how to wire up the starting button to the lamps. Ideally one button for two lamps, not that each lamp, each button. BTW it is that european wiring "series"... Need the diagram as fast as possible. Thanks!!!

Why the hurry? For one button to control two lamps, you need a momentary-contact normally open DPST (double pole single throw) switch. That's basically two pushbutton switches in one. Not hard to do as long as you can find the switch. That's not a common switch but not impossible, either. I don't have a way to draw a schematic "in a hurry" but can do so later if you wish.

I need it in like a week or so. My grandpa´s birthday is coming and I want to make a Letterbox with 2 f15t8/D backlighting the text...

Now that I know what switch, I don´t need the diagram until there are some resistors or so. But thanks for help!!!

Okay, sounds good! Hope the project goes well. Just a switch is all you really need. You won't need any resistors. If you wanted to be picky about it, someone might recommend a capacitor across the switch contacts, but that's a trivial detail in my opinion.

ok let make this simple.  i wire up preheat circuit
like you normally would with starters.  now just in place
of starters using a normally open switch to start the
lamp.  and place a normally close switch on the wire
leaving the ballast.  from that to input pin of the lamp
that way u can turn the lamp off like  desk lamp