ok brother which is it. The engine harness or upper electrical harness? When u stated fuse box that tells me upper electrical harness from the vehicle which is for power and some relays. If that's the case. Everything is color coded.
For the engine harness. There is a thread which has the skyline r33 manual in which you will find the ecu pin out. You will need the wiring schematics and the ecu pin out. It's quite simple. Match up the pin number to the color and then solder the items back together ensuring you use heat shrink for a protective coating. I do not recommend splicing. It will work but not a very trust worthy when looking towards longevity.
Shoot for continuity from end to end. Ecu pulg to sensor plug.
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[email protected] is not complicated at all. You simply need some direction.