OM3400 Exterior Lighting and Switches - Section 34 Page 34-5 Retard/Clearance Lights Retard/clearance lights (4) are dual function red lights. When the headlights are on, a low beam clear- ance light will illuminate. When the operator uses the retard function to slow the truck, a more brilliant light will illuminate to signal to traffic that the truck is slow- ing. Brake Light Brake light (5) will illuminate when the operator depresses the brake pedal. The red light signals to traffic that the truck is slowing.