TBH if you are not good with electrical diagrams I would get an auto electrician to look at it
On page 3-7 Engine control of the JDM wiring manual, you will see the FP ecu middle left of page. The +B power connection goes to pin 4 on the ecu. Follow the wire to the left hand side of page where it is labeled b, go back a page to 3-6 you will then see the wire from +B on ecu marked with a b on the far right of page. Follow this wire to the left hand side of page 3-6 and you will see it terminate in connector CK1, then onto connector AC2, then onto pin2 of R/B No.2 relay, that then connects to battery through pin1 of the relay and onto the R/B no.2 30A EFI no.2 fuse.
Hope that makes sense, if you follow the diagram in the manual it should. The manual also shows where the connectors are in the car.