HEAD 1894646 - Caterpillar

Do not conduct any service procedures on the DEF system until the DEF purge indicator lamp is not illuminated. The indicator lamp may remain illuminated for several minutes, even though the battery disconnect switch is OFF and the engine start switch is OFF. When the indicator lamp is on, the DEF system is still powered.
Never move the battery disconnect switch to the OFF position while the engine is operating. Serious damage to the electrical system could result.
The battery disconnect switch is inside the second cab.
Illustration 1 g00406959
Battery disconnect switch
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DEF lamp film
Battery Disconnect Switch - The battery disconnect switch can be used to disconnect the battery from the machines electrical system. The key must be inserted into the battery disconnect switch before the battery disconnect switch can be turned.
ON - To activate the electrical system, insert the disconnect switch key and turn the battery disconnect switch clockwise. The battery disconnect switch must be turned to the ON position before you start the engine.
OFF - To deactivate the electrical system, turn the battery disconnect switch counterclockwise to the OFF position.The battery disconnect switch and the engine start switch perform different functions. The entire electrical system is disabled when you turn the battery disconnect switch to the OFF position. The battery remains connected to the electrical system when you turn the engine start switch to the OFF position.Turn the battery disconnect switch to the OFF position and remove the key when you service the electrical system or any other machine components. Lock out access to the battery disconnect switch by closing the cover and installing a padlock.Turn the battery disconnect switch to the OFF position and remove the disconnect switch key after you operate the machine. This will prevent the battery from being discharged. The following problems can cause battery discharge:
short circuits
current draw via some components
vandalism