brake light mystery

[rustyrodknocker]

I'm chasing a brake light issue on my 87 c30 but having trouble with a good diagram.
Does anybody know if the white wire is the same white wire that runs up the column to the signal switch?
if so I may have a break in continuity between the brake light switch and the signal switch.
The brake light switch works. turn signals work. signal switch is a couple years old. looks fine. fuse good
I need to follow out the white wire but the diagrams I have found miss that one.
thanks for any help