sorry cant help with the wiring ,but im currently on the way to building mine just a few things you should look at to do .
change the fuel line under the car to a larger diamatre for better fuel flow also a front brake up grade does help alot kev rowley does a silvia brake upgrade for the front ..
when you cover the old hole for the shifter make sure your metal has a 40mm overlap this is required if you going to get it engineered .if you need anything just pm me theres a few diffs out there too that work well under the 120y too ,cheers geoff