If you are familiar with how the front brake switch is set up and how it works, the clutch interlock switch is basically the same thing on the other side. The switch is actually mounted in the left switch housing with a plunger sticking out (just like the brake switch on the right side). The first thing to check is to make sure the plunger is actually moving in and out when you engage and release the clutch lever. The switch could be loose inside the housing and the plunger not making full travel for instance. If the switch appears to be tight and working properly mechanically, then you will need to check the electrical function. It's just a simple on/off switch that should show continuity one way and an open circuit the other (I forget if it's normally open or normally closed).
Jerry
btw, one other possibility to think about, since you were in the fairing for the XM install, is that the wiring for the switch got damaged or disconnected. Check the switch continuity where the harness in the bars connects to the main or interconnect harness, not just at the switch itself. I don't have a wiring diagram for your bike, but if you need to trace circuits you will want to get your hands on one.