It's as easy as it gets! If you buy a load resistor with the blue Scotch-Lok connectors on the ends. One channel goes all of the way through-this is for the OEM wire that feeds the bulb connector, and one channel only goes 1/2 way through. This is for the stub end of the wire on the resistor.

These are referred to as "Insulation Displacement" connectors. The metal "W" in the center, when pushed/mashed down with a pliers, slices (displaces) the insulation on the wires just enough to touch the conductor inside. It does this to both wires at the same time-and: Viola! a circuit is made. The hinged plastic cover swings over and snaps closed to keep it together.

Put one of these contraptions on each of the 2 wires feeding the bulb socket, use a couple of tiewraps to anchor the resistor away from anything plastic, and that's it. They get warm, but they meet some MIL-spec for maximum jacket temp (130 Deg F?) so they won't damage any other wires, but they will mess up plastics. Like lenses.