The harness from the dash exits the cab above and to the right of the clutch pedal. That puts it near the left frame rail. The forward part of the harness goes along the inside of the left frame rail to just below the left side of the radiator where 3 wires for the left headlight go vertical along side the radiator to enter the headlight stand. The wires for the passenger or right headlight split off and go along the crossmember below the radiator and then go vertical along side the radiator on the right to enter the headlight stand. You will find holes in the frame and crossmember for clips to hold the harness wires, which should be enclosed within cloth loom. The vertical wires are also held in loom, and are held by clips attached to the radiator bolts.
Hope this helps,