First build: lefty TL-1L telecaster

[lotion5238]

You are right with that.
There is a small hole that comes through the back of the bridge pickup cavity. Your earth or ground wire comes up through that hole and is secured by the underside of the bridge.

also I am very confused about this diagram, the Neck, and pickup wires seem to have 2 inside of them, one is insulated and the other is not, how am I supposed to connect something like the yellow pickup wire because it seems to split in two?

I also forgot to ask, the jack is supposed to have a hot and earth wire but mine only came as a single one