Watch the Harp Style Licks online guitar lesson by Brad Carlton from Guitar Lab: Boogie-Woogie
This lesson utilizes the fifth string open as the 5th of the boogie-woogie pattern. Therefore we are in the key of D and the 6(B) is available on the sixth string. The b7(C) will be in the third fret of the fifth string. This layout allows a "let ring" scenario to the 5-b and b-b7 intervals. The root is implied in this lick. This lick is dark sounding because we are so low in register.