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Old 08-18-2003, 07:50 PM
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Join Date: Oct 2000
Location: Oakland, CA USA
Posts: 221
Battery question

This is really just curiosity more than anything else...
Most of my friends cars (various Japanese and American makes) have a line going from the negative terminal on their battery to the chassis and engine block. My car (1987 560SEL) only goes to the chassis. So...what's the difference? Is there an advantage (or at least a reason) to doing both (engine and chassis) versus one? This is bothering me.
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Old 08-18-2003, 08:15 PM
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
Mercedes has a seperate ground cable from the engine block to the chassis. It's under one of the bolt heads on the bellhousing.

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Old 08-18-2003, 08:25 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,010
The heaviest current draw from the battery is the starter motor, so on many cars, especially older cars, the negative cable attaches to a starter motor mounting bolt, which provides the least resistance path back to the battery.

Such a wiring scheme would also require a good ground between the engine and the chassis to ground the various lamps and accessories. The alternator usually grounds to the engine through its mounting brackets.

In a case where the battery ground cable connects to the chassis, you should also find a substantial ground cable from the engine to the chassis to handle the 100-200 amp draw of the starter motor, and the up to 120 amps from the alternator.

Most cars usually have more grounds than absolutely necessary for electrical continuity. The extra grounds are usually there to reduce electro-magnetic interference that can be caused by high loop currents.

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