I too have the 18 circuit kit, was like $225 at Summit a long time ago. Some engineer-types have said it's a waste of money, but to a non-engineer like me, it was well worth it.
It comes with basic instructions, this wire is positive to the headlite, this wire is positive to the parking lite, etc. It doesn't tell you how to connect to the Datsun stuff. You need a stock wiring diagram (good luck with it!) to find out which wires to keep and which to pull.
Owen