They should be working.

I tested the 757 III in FSX-SE, P3Dv3, and P3Dv4, and the Aircraft Landing-lights illuminate ground option with the checkmark, and without the checkmark.

Without the checkmark in FSX-SE, and P3Dv3, the taxi lights and landing lights didn't illuminate if I did this.

Without the checkmark off in P3Dv4, it made no difference, the taxi and landing lights still illuminated th ground.

Try reinstalling (repair option). Make sure you disable/turn off your AV, and that you run the installer as an administrator.