Harley has actually had a similar harness in the P&A catalog for awhile now:
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Independent Control Auxiliary Lamp Wire Harness Kit
Maximize your nighttime view down a lonely stretch of back road. This simple to install wiring harness permits independent control of your bikes auxiliary lamps, and allows the lamps to be switched on when the headlamp is in either low or high beam settings.
69200441
Fits '98-later Electra Glide®, Street Glide® and Trike models equipped with auxiliary lamps.
MSRP US $29.95
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Anyone with some basic wiring skill and a soldering iron (I personally prefer soldered connections rather than crimp) can easily do the same thing at nearly zero cost. The little harnesses work out fine for those who prefer a simple plug and play approach.
Jerry