When you change it, I suggest you coat the contacts with silicone di-electric grease, especially since you are in Canada. You might also spray contact cleaner in the connector terminals. Don't throw your old light switch out since it probably just needs contact cleaner sprayed on the reostat wire to fix the brightness adjustment.
One thing I don't understand is why the dome light works (full-on click position), but not the dash lights. Maybe the dash lights are always on the reostat, so a different path. Anyway, you must pull the headlight switch to trouble-shoot, so swap parts and see.