1. Make sure the car is in "Park" or "Neutral."
2. Turn the headlight switch to the "On" position. The headlight switch is located on the left side of the dashboard.
3. Turn the dash light dimmer switch all the way clockwise. The dash light dimmer switch is located on the left side of the dashboard, to the left of the headlight switch.
By turning the headlight switch to the "On" position and the dash light dimmer switch all the way clockwise, you should be able to turn on the dash lights in your 1993 Mercury Grand Marquis.