Dash lights that dim intermittently

Dash lights and radio lights dim intermittently.The dealership tried replacing the dimmer switch,and there are no codes stored in the computer. It does not correlate with amount of time the car is driven. It happens quickly as if a switch was thrown and not a gradual decline. The car is a 2009. Does anyone have any ideas?

Not being familiar with the Equinox, is the dimmer switch part of the main lighting switch? Or headlight switch if you prefer to call it that?

If the main switch is a separate one then I would suspect a circuit is failing in that one. The main switches in many vehicles often have a separate circuit providing power to the dash lighting so it’s possible to have dash lighting affected with no affect on headlights, etc.
It’s possible that depending on the circuitry the outside park lamps may also be affected by this problem.