BAR 1978594 - Caterpillar

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Brake light system component connectionsThe Machine Control ECM will monitor the pressure in the brake system using the Service Brake Pressure Switch. When the pressure in the system is greater than 500 kPa (72.5 psi), the ECM will turn ON the sinking driver for the Brake Light Relay. This will allow system voltage to be directed to the rear brake lights.If the left armrest is in the raised position as indicated by the armrest position switch, the ECM will not energize the Brake Light Relay when the pedal is pressed. When the service brake is initially locked as indicated by the Service Brake Pedal Limit Switch (switch circuit grounded), the ECM will turn ON the output for the brake relay. After 60 seconds, the ECM will turn OFF the output for the relay. The ECM will resume normal brake light operation when the Service Brake Pedal Limit Switch indicates that the brake is no longer locked (switch circuit not grounded).