My 03 ultra had same issues. Speedo worked intermittant. At one point speedo would stop working when I had to turn handle bars to the left. Would work when I turned them to the right. All 3 wires to bus were broken just in front of the steering neck.
I believe the turn signal module uses inputs from the vac (to turn turn signals off after a predetermined distance is traveled or the bike is leaned in a left or right turn.