Attach the end of this new 3-wire loom to the ends of the old wires by wrapping and taping them together, then from inside the wheel-well pull on the old wires, back from the bulb area back into the wheel-well. Push the end of a coat hanger from the engine area through the wiring grommet (in the front corner area) into the wheel-well area, then attach the end of the coat hanger to the 3-wire loom and securely tape together.
Carefully pull these wires back through the grommet into the under-hood area (It's a tight 15mm fit, so use some WD-40 or Vaseline to lube and protect the grommet and the tape on the new wire loom). Detach the ends of the new wires from the old wires, then cut into the old loom a couple of inches and cut off the old wires back in the old loom. Back at the headlight buckets, ensure that un-taped wire ends run through section of 15mm flex tubing in hole in headlight mechanism (to avoid chafing during rotation).
If a 3-wire detachable connector is used here (preferred, as it allows future removal without cutting wires), install it and solder or connect wires to the 3-prong type headlight bulb connector. Make sure wire colors are in correct location at headlamp bulb (see Diagram, at Right).
Repeat wire replacement procedure on driver's side of car.
Then, for a clean look, use the black wire ties to neatly secure the new passenger-side loom to the old harness, where it goes in front of the radiator and back towards the master cylinder. You can also wire-tie the driver-side harness where it crosses under the master cylinder.
Separate brown (ground) wires from ends of the new wire looms near the Master Cylinder, then splice the yellow wire and the white wire to the existing wire harness. You have 2 options for location: The easiest to access, is on the main harness in the driver's side of the engine compartment, about 10" towards the rear from the radiator support beam. Unfurl the metal clips, then pull the main harness out from under the inner lip of the fender. The original splice location is near the master cylinder (where original wires connect 2-into-1 in the loom) but unless you insist on originality, it's a tight area for the splicing and soldering work.
Open up the loom, by cutting sleeve lengthwise about 8" with an exact-o blade, then locate, tug out and cut the white wire and yellow wire (forward of area to be spliced). Prepare to splice the ends of the replacement white wires to a small section of the original white wire (use blade to strip a 1" area of insulation, or two separate ½" areas "staggered" for a cleaner look). Place some cardboard below the area for protection, then carefully solder (using lots of flux) these wires together. Let cool, then use this same approach but about 1" back , to solder the replacement yellow wires to the original yellow wire. Let cool, then tape up the loom, and hide the splice area by securing it with the clips under the inner lip of the fender.
Connect brown wires to chassis ground, by adding a round "eyelet" to wire ends and attaching with self-tapping screw to existing hole in engine area sheet metal (& sand off rust/paint there) on inner fender-well behind master cylinder (see photo).