ECU hold power

Hi- im wiring a link G4+ to an old car . The ignition switch momentarily loses power when the key flicks back from start to run . Will this effect the ecu at all or will i have to enable the ecu hold power function ? If so can someone walk me through the process . ? I have a positive power source from the ignition switch when the key is in the run position . Where to from here ? Thanks- Ken