Tech Tips

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Electrical System

DO NOT DISCONNECT THE BATTERY WHILE THE ENGINE IS RUNNING!

On older vehicles with mechanical voltage regulators, it was a common practice to "pull" a battery cable while the engine was running. If the alternator was charging, the engine would keep running. If the alternator was not charging, the engine would stall. While this practice was not recommended, it didn't seem to do too much damage.

Such is not the case with electronic voltage regulators! Everyone knows what a voltage "surge" or "spike" will do to a computer. The modern automotive electronic voltage regulator has some of the same components as a computer. Pulling a battery cable while the engine is running will send a voltage "spike" throughout the electrical system of the automobile. This can, and usually does, damage the voltage regulator as well as other components such as the engine management electronics, ABS control unit, and electronic dashboard display. In fact, many new automobiles have specific instructions regarding the grounding of your body to the chassis of the car to prevent static electricity when working on delicate electronics. If they are this sensitive to static electricity, just think what could happen if a battery cable was disconnected!

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