Not long after I got my 260z, I bought a loom off eBay to use as a live diagram to help through my numerous electrical issues. A bit extreme, but it worked.
Not sure if it will be of much help but I fished it out and had a quick look. On the first photo is shows that the white wire goes into a black sheath (well mine doesn't, its come away) and it turns into the thin black wire you can see that becomes a spade connection then disappears into the loom.
As Mike said, it turns into a white/red cable and comes out into a block connector (where the negative multimeter probe goes into in the second picture).
The third picture shows a close up of the other colours in the block to help trace yours.