main relay

enjoying this lots of great little tips and nice to know for the better part i have been doing most things right :)

one question is regarding the the way you did the main relay in this tutorial! i dont fully understand why you essentially have 2 main relays that both just turn on together? I usually have one highside driven main relay from the key for the ecu, injectors, ICV, plus any other solenoids, relays and sensors etc. Then another one for the Ignition coils so they have a nice independent supply (i do mostly 6 and 8cyl engines) and of course last one one for FP. IG and FP relay coils feed from the main relay. I thought its always best to have at very least the injectors and ecu together so they see the same voltage and coils separate because they generally have quite large current draw and also keep any noise away.... but am i potentially creating a possible back feed situation?