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  #1  
Old 10-15-2019, 03:19 PM
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What Gauge is a Stock 84 300D Battery Cable

For some reason a Battery Cable Gauge is measured with the insulation on; see attached picture. Mine measured .410 outside diameter which is slightly smaller then 2 gauge.


The actual wire core was .25

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What Gauge is a Stock 84 300D Battery Cable-battery-cable-gauges.jpg  
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Old 10-16-2019, 05:16 AM
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I find original was 4 gauge 100% copper J1127-S GT
New ons on ebay are updated to 2 gauge or 12 gauge to 10 gauge
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Old 10-17-2019, 12:46 AM
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Quote:
Originally Posted by optimusprime View Post
I find original was 4 gauge 100% copper J1127-S GT
New ons on ebay are updated to 2 gauge or 12 gauge to 10 gauge
I found it odd that on the chart that I posted the insulation appears to be part of the diameter measurement. If I go by that the original cable with the Mercedes logo on my car is slightly smaller then 2 gauge.

If the gauge in the chart went by only the copper wire core the stock cable the a 6 gauge cable would be thicker then the stock Mercedes cable.

I was thinking on replacing the Cable. I peeled back the cable insulation as in the attached picture. And found as you see it.

After soaking it in water and baking soda to get rid of the white corrosion the cable looked OK and the part that is inserted into the clamp had also been soldered so there was no corrosion in there. So I just elected to glue the insulation back on with silicon sealant and wrapped it with rubber electrical tape.

Since the positive cable has been working fine since 1984 and there was no apparent damage to it I felt no need to update/upgrade it.

But, I decided to post the info from the measurements because I cannot recall anyone ever saying what measurement the stock cable actually was.

Note I just finished replacing the brushes in the Starter which made me think of replacing the Batter Cable if needed.
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What Gauge is a Stock 84 300D Battery Cable-battery-cable-insuatation-peeled-back.jpg  
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Old 10-17-2019, 12:49 AM
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Quote:
Originally Posted by optimusprime View Post
I find original was 4 gauge 100% copper J1127-S GT
New ons on ebay are updated to 2 gauge or 12 gauge to 10 gauge
The higher the gauge number is the smaller the thickness is.
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  #5  
Old 10-18-2019, 04:59 PM
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That cable look to be in poor condition, you can refresh this to better than original quality with an elbow battery clamp and some fine stranded 2 awg copper cable.

There are some online places that will sell you a custom made one, or if you can find a HD truck battery shop, they have hydraulic tools, clamps and lugs to make new cables, that can be a local solution.
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Old 10-18-2019, 07:43 PM
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Originally Posted by Zulfiqar View Post
That cable look to be in poor condition, you can refresh this to better than original quality with an elbow battery clamp and some fine stranded 2 awg copper cable.

There are some online places that will sell you a custom made one, or if you can find a HD truck battery shop, they have hydraulic tools, clamps and lugs to make new cables, that can be a local solution.
It turned out to be just surface discoloration. I am already done with it.
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Old 10-20-2019, 11:57 AM
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Wonder if Mercedes made them to some metric standard instead of US wire gauge?
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  #8  
Old 10-20-2019, 08:36 PM
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Yes, mercedes use metric wire size of sqmm rather than awg
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  #9  
Old 10-23-2019, 11:27 PM
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Got my starter that I replaced the brushes on back on the Car and it fired up with zero issues. Not unexpected since the original positive Battery Cable has caused no issues since I owned the Car.

I can understand replacing a cable that has issue but I am not seeing any need for a thicker cable. I mean if the original battery cables were sufficient when the Engine was new and tight and had more resistance to turning why would you need a thicker cables on an old worn engine that turns easily.
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Old 10-24-2019, 08:27 AM
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Originally Posted by Diesel911 View Post
Got my starter that I replaced the brushes on back on the Car and it fired up with zero issues. Not unexpected since the original positive Battery Cable has caused no issues since I owned the Car.

I can understand replacing a cable that has issue but I am not seeing any need for a thicker cable. I mean if the original battery cables were sufficient when the Engine was new and tight and had more resistance to turning why would you need a thicker cables on an old worn engine that turns easily.
To me, the theory would be that you had to replace brushes earlier than otherwise because you had higher current than necessary because your series resistance of the battery through that smaller cable was higher than it would be with a larger cable. More voltage drop.

Now, thatís the theory. In practice, unless cranking long times consistently and repeatedly, including when heat soaked, it probably doesnít much matter until the point where the cable is corroded inside the insulation.

Iíd be more concerned with good and more grounds than the positive cable.
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  #11  
Old 10-24-2019, 12:38 PM
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Originally Posted by JHZR2 View Post
To me, the theory would be that you had to replace brushes earlier than otherwise because you had higher current than necessary because your series resistance of the battery through that smaller cable was higher than it would be with a larger cable. More voltage drop.

Now, thatís the theory. In practice, unless cranking long times consistently and repeatedly, including when heat soaked, it probably doesnít much matter until the point where the cable is corroded inside the insulation.

Iíd be more concerned with good and more grounds than the positive cable.
The test for if you need a new Battery Cable or the contacts need cleaning I have never seen anyone do since starters are sometimes hard to get at. You hook a volt meter (I don't know if this is good to do with a typical volt meter. Likely better with a dash board type volt meter) one end on the positive cable and one end on the Starter Terminal the other end of the batter cable attaches to.
If everything is good when you crank you should see no voltage on the volt meter. If your Cable or contact area have resistance you would see some voltage.

I think this is the original starter from 1984 and I have owned it since 2007 which is 12 years of mostly city driving meaning lots of starts. 12 year by itself is a good run for a starter.

So if you buy a Battery cable the same length it is likely made for the American market and is 2 gauge and a little fatter then the original.

See that attached pic. Every wonder where the worn off part of your brushes goes?
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What Gauge is a Stock 84 300D Battery Cable-crap-worn-brushes.jpg  
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  #12  
Old 10-25-2020, 12:27 AM
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Thought I would give this year old thread a bump.
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  #13  
Old 10-27-2020, 02:14 AM
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If you gave it a bump for unsolicited advice Im down. Replace that battery cable.
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  #14  
Old 10-28-2020, 12:13 PM
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Quote:
Originally Posted by 240D.Bill View Post
If you gave it a bump for unsolicited advice Im down. Replace that battery cable.
I agree. Cables are cheaper than starters, and keeping the resistance down and the voltage up keeps the starter working.



My trucks have a little bit bigger engine, and use a mix of 2/0 and 4/0 cable for the battery to starter circuit. It works, but I wouldn't go any smaller than stock on them.


These little Mercedes engines use such short, inexpensive cable runs it would be silly not to go bigger than stock. I certainly wouldn't go smaller than #2, and wouldn't hesitate to go bigger.
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  #15  
Old 10-29-2020, 11:53 AM
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In this site there is a diagram which I will also attach on how to use a voltmeter to see if your cable and connections are OK or not. As a good way to troubleshoot. (You will need someone else to do the cranking or at least it will be easier that way.)
Even if Battery Cables are fairly cheap why go through the expense and the labor to change a cable that does not need to be changed.

https://www.hagerty.com/media/maintenance-and-tech/measuring-voltage-drop/
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What Gauge is a Stock 84 300D Battery Cable-checking-battery-cable-voltmeter.jpg  

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