. OPERATION EXPLANATION OF COMPONENTS INTER-AXLE DIFFERENTIAL LOCK PILOT LAMP lights up when the inter-axle differential lock is lockup is 3 - 20 RETARDER PILOT LAMP This monitor (2) lights up when the retarder control lever is pulled and the r etarder is actuated. This monitor (3) actuated LOCKUP PILOT LAM This pilo t lamp ( 4) orqu engaged and the transmission i s shifted to d irect drive SHIFT HOLD PILOT LAMP This monitor (5) lights up when the shift hol d switch is actuated.