. OPERATION EXPLANATION OF COMPONENTS differential lock is lockup is 3 - 20 EXHAUST BRAKE PILOT LAM (If equipped) This monitor (2) lights up w hen t he exhaust brake i s actuated. RETARDER PILOT LAMP This monitor (3) lights up when the retarder contro l lever is pulled and the r etarder is actuate d. INTER-AXLE DIFFERENTIAL LOCK PILOT LAMP This monitor (4) lights inter-axle actuated LOCKUP PILOT LAMP This monitor (5) lights torqu converter engaged and the transmission i s shifted to direct d rive.