Switched 12v source

If you tie the blue and brown together is there any harm with the power back feeding to the ingintion switch (IGN 2)? I'm about to wire up my car and wanted to know the safest, easiest most economical way of wiring a FI Tech. With a factory ignition sounds like diode/relays would be best bet. Does anyone have a wiring diagram of how to accomplish this? @Johnny Mac