#CJam, 92 bytes
This is based on a recursive flood fill explained here and can be golfed a lot!
q~:Q_&{:IQ3/S*Sca5*+:T;G,G*{:AT=1$={[WXZ5 4_~_)_)]Af+Tf=AT='#a+&,g{TA'#t:T;}*}*}%;aT\/,3<},p Requires the input in order of ABCDEFGH like:
[0 1 1 2 1 0 5 5 1] and output is the connected nodes:
[1 2 5] Full explanation to follow