I've just had this conversion done, it's the differences in the looms which I have worked out some and the others done by the engine builder:-
1) Trace speedo wiring, and swap pins where necessary.

2) There is no ign power feed to the abs ecu

- loom differences

- trace and swap pins
3) JDM loom has no wiring for rear fogs, but has extra earths, which causes the brake light circuit in the front uk loom to earth thru the brake light system.

Needs a wire snipping on the JDM loom, or alternately put a wire thru the car so you can re-enable the rear fogs from the std Toyota switch.

4) Probably no oil level switch plug on the rear JDM loom.

Ironically my low oil light is intermittent, not sure what's causing tha since I dont have an oil level switch!!