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Need advice RE 37 Stude Dictator positive earth battery charge system.


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Hi, as the title suggests, I require some info and advice about my '37 Studebaker Dictator and its battery charging system.


Background on me.

    Western Australian (no the blood has not rushed to my head 🙃)

    Not shy around mechanical and most electrical work on vehicles,

    I have a few vintage cars and tractors I do all the work on myself, just never tackled this particular system type before, all my others are 12 volt neg earth.

   I have the wiring diagram ( hopefully see attached, If I get the upload right)


Background info on the car.

   37 5A Dictator.

   Positive earth 6 volt system.

   New 920 CCA battery.


Reason for wanting the info.

    Moving the battery into the boot due to the larger size of the new battery.

    Kinda confused as to how the battery gets recharged.


The Nitty Gritty.

  As previously stated moving the battery but I cant find any charge wire/track from the generator to the battery to recharge said battery.

  Even on the wiring diagram there isn't one so I'm hoping someone can explain it to me.


The only thing I can think of is that it recharges through the body of the car, But I'm unsure if my logic is sound.


Regards and Thanks in advance.


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The current flows in a circle on any system, positive or negative earth. It doesn't really matter which post of the battery is connected to earth, as long as the rest of the equipment is designed to match.


In the diagram above battery charging current flows from the generator, through the ammeter, to a connection at the starter post, to the battery, from the battery to earth (meaning the chassis, the body, engine, straps, etc., all electrically connected together) and from earth back to the generator again.


On a negative earth system the current would flow in the same circle, just in the opposite direction.


Edited by Bloo (see edit history)
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Power goes to the battery by way of the ammeter. It has to be this way if the ammeter is to register the charge/discharge or +/-.

On the wiring diagram you can trace the wire from the generator to the ammeter, ammeter to starter, starter to battery. The wire from the ammeter goes to the battery cable on the starter but it might just as well go straight to the battery. They probably did it that way to save wire.

Edited by Rusty_OToole (see edit history)
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The diagram is not clearly drawn. The A wire leaves the generator probably thru the little box on top that is probably the cutout relay, or usually just called the cutout. That device disconnects the GENERATOR from the

battery when the voltage leaving generator falls below a low value. So the battery wont run down and or cook the generator when engine is not running. The A wire connects to the left side of ammeter, and not shown on diagram connects to right side terminal of ammeter. (All current flows thru the ammeter). Wire 5 (I think its a 5)

leaves there and ties into terminal on STARTER where battery cable is attached. Or possibly spliced into the battery cable at some point.... That completes path to BATTERY  - terminal . Then as others said the BATTERY + terminal attaches to chassis, the common tie point for all the other devices in the system.  I hope this helps you. And cheers from Texas...

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Great car, but then I'm a bit biased since I own two 1937 Presidents, both a sedan like yours and a coupe. One of the most stylish cars of the "fat fendered" late 40's. I have a question though, why the battery in the trunk (boot)? Twenty years ago when I got the sedan that I own the previous owner had moved the battery(s) into the trunk-he had two. No matter how much I tried to tweak the system I could not get the needed starting power. Heavy ground cables, good ground, new batteries (two Optoma's). Finally out of desperation I repositioned one Optima under the seat where it belonged and walla it was like a new car. I had replaced sixty pounds of battery with one sixteen pound battery-I never looked back. I'm interested in why you made your choice to make the move?



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Hi guys thanks for the replies, they have allayed my concerns.


@Buffalowed Bill, absolutely love the car, had it for a few years now and has always been hard to start from cold, so I have purchased a stronger cold crank battery but it is larger than the battery box under the seat,

   by about an inch, so instead of modifying the box I'm installing it in the boot.

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You will need some LARGE copper to connect the battery to the starter terminal since it will now be, what, twice or three times as long as the original wire?


Here we would say 4/0 (pronounced four ought) AWG cable.  That is around 107 mm² in metric size cable.  I use 2/0 for short under hood runs when I make cables. Larger than 4/0 is not practical around here, as it is not usually at the welding supply house. 

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A 6 volt system is a reliable system as long as all contact points in the starting and charging systems are clean and shiny, free of dirt, grease, rust and paint.  Make sure any body to frame ground straps are in good condition, they can be overlooked.

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Do not put the battery in trunk. Take the battery you bought back and buy a 6v OPTIMA. Lay it on its side and make a cover out of metal or plywood and paint it black to hide how ugly they are. Clean all grounds and contacts, even your starter. I have this set up in all my cars. They are the best 6v battery you will ever buy. 

Edited by paulrhd29nz
Poor education (see edit history)
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I wish you the best of luck whatever you do, but IMHO the extra cable length will be a bigger problem than a slightly smaller battery. As others have mentioned, the cable will need to be huge.


2/0 cable should be more than adequate (and is a good choice) with the battery in the original location. If the negative cable goes to the starter (in a positive earth system), the positive cable will go either to the engine/transmission assembly or to the chassis.


If positive goes to the chassis, then there needs to be a third cable or strap, every bit as big and good and clean as the other two, running from the chassis to the engine transmission.


If positive goes to the engine/transmission, then there still needs to be a wire or cable from the chassis to the engine/transmission, but it can be smaller as it is not carrying starter current.


Optimas are a screwy shape, but have more cranking amps than a 1930s car battery and usually fit in the available space. Some folks use 2 Optimas in parallel, and it still fits in many battery boxes. 2 should not be necessary on a Dictator.


Edited by Bloo (see edit history)
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1 hour ago, Bloo said:

Optimas are a screwy shape, but have more cranking amps than a 1930s car battery and usually fit in the available space. Some folks use 2 Optimas in parallel, and it still fits in many battery boxes. 2 should not be necessary on a Dictator.

I agree completely with @Bloo.  I use a pair of Optimas in my 8-cylinder Pierce-Arrows, but primarily for charge-deficit nighttime running.  A single Optima does the job in my 1918 Pierce with a 525 cid engine, since that car doesn't have long lights-on runs.  Optimas are particularly good for underseat or underfloor installations because they never need water, don't produce corrosion, and emit no corrosive gas--and need not be charged during an overwinter nap.


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Hey guys, thanks for all the replies.


@Frank DuVal,  Yeh have gone with what is known here as 2 B&S, according to an auto electrician that is more than enough so have gone with that.


@dictator27 Yep all contact points have been cleaned and "made good".


@paulrhd29nz@Bloo@Grimy  Haven't heard of that battery, will look out for it, the longer leads are working fine, car starts very easy now, have not mounted the battery yet

so may look at the optima before drilling any holes.


It turns out that the battery the local shop has been supplying for the last several years is made for forklifts so that may be why it is so slow to turn over when cold, we will see if I can find the optima anywhere.

I can always use the leads for my old tractors when I get around to redoing their wiring  ;)

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Remember, it is not the current carrying ability of the size of the cable, it is the voltage drop that is the big issue.

I looked at Jay-Dee (Australian) website and found this table:

Auto Size

Nom Area mm2

Nom O.D.mm

Amp Rating

Part # Prefix

Gauge Guide

8 B&S






6 B&S






4 B&S






3 B&S






2 B&S






1 B&S






0 B&S






00 B&S






000 B&S







I then looked up an AWG to mm²:

AWG                                                                                                                                               mm²

4 25
2 35
1 50
1/0 55
2/0 70
3/0 95
4/0 120


Based on this data, I would say you need 00 B&S to trunk mount a 6 volt battery and have it work in all weather and starting conditions.


But, you say it is working  with #2 B&S.  😉



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