I want to add a spot lamp switch to my flhx. Can I plug switch wires into existing harness to power up switch and plugs in fairing for spot lamps like on the Electra glides or do the flhx's not come with same harnesses?

 

Most wire them in to wires in the faring.
However your accessory switch has two poles that are hot all the time two that are controlled by the switch. so if you wanted to run an always hot wire off it that would be simple to do. In my case the always hot wires run spoiler lights and ficsa lights, switch runs a lenale fan.
Here is some pictures of the plug and an a adapter. A simple Y cable can be made or purchased

 

I would like to.wire auxiliary lights to spot lamp switch so they will go off on high beans but do not know how to wire it on my flhx