I have a dohc1990 240sx hatchback with a chassis harness from a dohc 94 coupe convertible with a manual ECU from 90, and a engine and lower harness from wiring specialties.I just need to know any differences like wiring or if it would work and I have these questions would a neutral switch shut off ignition or just prevent starter. Do I need anything on the inside plugs in besides the wires to key ignition and ecu basically I just need to know what’s required for a start up with all these components

Also I’m pretty new to this stuff so any tips or suggestions would be appreciated I’m not a fan of wiring because I could risk a lot of components