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My jeep's stock wiring has two ground cabled coming from the negative terminal. I recently upgraded all of my positive cables, and now I'm on to the negative. Is it necessary to have one cable going to the engine, and one going to the frame - or would one large wire going to the engine, since the engine is connected to the frame, work?

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Normally when people upgrade a ground system, they add ground wires. If you're considering removing any of them, you're definitely not doing an upgrade... Generally speaking on car projects, if you find yourself using the term "Get away with", you've probably strayed off the upgrade path and are more likely to be downgrading... –  Brian Knoblauch Apr 20 '13 at 13:19

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The frame ground is needed. Although the engine is bolted to the frame all the connection points are isolated hence insulated by rubber. The reason for the rubber mounts is to isolate the engine vibration and the resulting stress from the frame. Some older vehicles did use a single ground to the block. This required a second ground wire from the block to the frame or chassis. A possible reason for the switch to a frame/chassis to battery ground connection is the increase in electronics that require a more secure ground.

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The reason I asked about the engine bay is because I upgraded from an 80amp alternator to a 160amp alternator. –  kjmccarx Apr 20 '13 at 14:57

You should maintain both ground wires. If you removed battery to chassis you would have to add engine to chassis wiring. The battery to engine wire is there to ground the alternator.

Battery to chassis wiring is probably a safer, shorter, and easier run than engine to chassis anyways so why bother.

You probably want 2gauge wire all the way around. You could probably "get away with" 4gauge but I by no means recommend it since I am not an electrician.

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Yes. I added a 160amp alternator - I wired it with 0awg welding cable (the real stuff, not the ebay stuff). I could only afford enough for the posative wiring at the time, but I am going to add 0awg ground wire to at least my engine (for the starter and alternator) and maybe to my chassis, as well. –  kjmccarx Apr 23 '13 at 1:45
    
@KeeganMcCarthy, there's no question about "maybe to my chassis" - you will install that cable, now or later. Not only one to the chassis, but one to the tub, too. EDIT: You do understand what a 160A alternator will do to your gas mileage, right? Or rather what using it to its full potential will do to it... –  TDHofstetter Aug 29 at 0:37

Just add more ground/earth cables, wherever you can. Shorter the better too. Ive added a larger battery to chassis, battery to block and everywhere that makes sense/is out of site, ive added in more chassis to block cables etc... Every bit extra helps.

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Yes, you need both grounds. I had a 1963 Oldsmobile giving to me. The person could not fix it. Every time it made a right hand turn, the car would die. He took the dash apart looking for the cause and did not find anything. I got the car and first thing I saw was the ground strap to the engine was broke. Just by making a turn the strap came apart and the car would die. I put a jumper cable on frame and engine. I drove it back to owner's house in 30 min. He was not happy. I got it working. Nice car. It was a 2 door Jet Star.

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