If ford is still using the same circuit design in the 2006 as they did in the 2001 the power flow is from a 30 amp fuse in the BJB that feeds both low and high beams. The low beam circuit splits to the light switch, which then routes power through the multifunction switch, then back to two fuses (RH & LH low beam) in the BJB, then on to the individual headlamps. The high beam power runs from the same 30 amp fuse directly to the multifunction switch, then back to another fuse in the BJB, and then to both high beams.
Most likely cause: bad connection, light switch, multifunction switch.
2001 Ranger Edge 3.0 V6, 5 speed M/T
Limited Slip Differential, James Duff Traction Bars
Kumho 30x9.50 15 MT / Black 297 Series 15x7 Rims