(papajam learned me the word

)
The main relay gets triggered by the drive relay after it activates, so you end up with:
Engine turns, ignition fires.
Ignition fires, pulsing/tach-like signal (get it? Tachymeteric?) gets sent to drive relay via the ignition coil.
Drive relay comes on and fuel pumps begin pumping, while simultaniously a steady/non-pulsing '+' trigger signal goes from the drive to the main relay so it comes online which in turn allows the injectors to fire when the ECU starts pulsing the injector '-' signals through the brainbox proper.
EDIT: Will the drive or main relay affect ignition spark? No, not as far as I'm aware of, as they are activated
by ignition spark, so they cannot be in control of it. (well, one is activated by spark pulses and it controls the other, so no spark, no activation of either relay)
The L-jet stuff piggybacks on an existing functional system. All it does is control fuel.
Now perhaps the motronic ignition box would have a more significant effect on actual firing, (though the engine can be made to run happily without it using a free-standing aftermarket system), but not the L-jet fuel setup.