I suppose youve come across Service tips, at BryantRV
http://bryantrv.com/docs2/docs/servtips.pdf.
It also identifies (p.25) the eyebrow wires color location/pins on main & upper board (but not function as you noted-) between the 2 which/wher to test.... Curious where you found that? It mentions the PAL-but sure sounds like outlined tests are with meter? Few simple tests on main/uppper and cable.
Not knowing I assume that main board feeds the eyebrow power which in turn tells main board what to do? Curious it mentions a failure mode if eyebrow fails and should continue to run, never noted that.
Not much help but more info if you hadnt already found.