With the harness you only need to use one stock power connector, and the other bulb draws power from the harness.
So basically the harness gets its power from one stock bulb power connector and the battery itself.
You'll end up having one stock bulb power connector dangling.
1989 Accord Coupe, 260k+ miles & going.
2011 Insight EX, 180k miles, RIP.
2012 Lexus CT200h, 80k+ miles & going.