How about the instrument light dimmer? Has nothing to do with headlight dimmer. Surprised if you even have instrument lights. However, someone may have replaced the switch before and just left that on the floor.

 

I have to file this one away as 'never going to know'. Everything works as it should. It may just have been a part that was stuck up there in the wiring harness from previous work and my changing the instrument panel simply knocked it down.
Thanks again for all the responses.