Headlights dimmer switch location needed

The selector switch is in the steering column as part of the multi-function switch. However all that switch does is send a signal to the BCM to select either the high or low beam relays located under the hood in the junction box in the left rear. Each relay also has it's own fuse in that same box. So if say both high beams were out but low beam works I would start with the high headlamp fuse then the relay and test those first. What is the issue you have?