MOTOR AS 3639459 - Caterpillar

Grounding Practices
The electrical system for the vessel and the engine must be properly grounded. Proper grounding is necessary for optimum engine performance and reliability. Improper grounding will result in uncontrolled electrical circuit paths and in unreliable electrical circuit paths.Uncontrolled electrical circuit paths can result in damage to the following components:
main bearings
crankshaft journal surfaces
aluminum componentsUncontrolled electrical circuit paths can also cause electrical noise. Uncontrolled electrical circuit paths may degrade the performance of the vessel and of the radio.The following systems MUST be grounded to the negative "-" battery terminal:
the alternator
the starting motor
all other electrical systemsThese components and these electrical systems can be grounded to the negative "-" terminal in one of two ways:
direct
indirectNote: The alternator and the starting motor must also meet marine requirements for isolation.There is a direct method for grounding systems and for components. This method involves running a ground wire between the component to the negative "-" terminal. The indirect method accomplishes the same result. For engines with an alternator that is grounded to an engine component, two conditions must be met:
A ground strap MUST connect that component to the negative "-" battery terminal.
The component MUST be electrically isolated from the engine.A bus bar with a direct path to the negative "-" battery terminal is permissible. This is also recommended for use with all common ground connections.