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Negative Ground


rereaves

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6 hours ago, busycoupe said:

The brake light switch on a 48 Dodge is on the bake line in the vine compartment on the driver’s side just below the horn relay.

Thank you for all your help. I now have turn signals they are very weak. I pulled the headlight beam and found no power. Tried exercising the dimer switch no luck. Bulb looks ok but without power who knows. Will continue to trace wires. Again thanks

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21 hours ago, Andydodge said:

US cars when they were 6 volt were Positive Earth......when they went to 12 Volts they changed to Negative Earth..........as for the non  working lights I'd be checking the light switch as all lights should take their power from that switch.........do you have a workshop manual with the wiring diagram?..........as your car is 6Volt then it SHOULD be positive earth.......I'd be starting over from scratch, checking the generator, regulator & starter, they should have their voltage on them..........the actual headlight switch, dimmer switch and amp gauge don't care whether they work on 6 or 12 volts, the original Fuel Gauge will need a voltage drop or resistor wired into its power circuit if the cars 12 volt..........all the globes should be the same voltage as the battery voltage............then go thru all the earth connections, check any fuses that have been added, generally speaking these mopars usually only have one fuse in a holder attached to the headlight switch and when it blows All lights are affected but who knows whether someones added a couple of extra fuses.......thats why the wiring diagram comparision to whats actually there is worth doing..............lol.......welcome aboard from Oz BTW...........lol.......andyd.      

Great feedback, I will follow your suggestions. Looks like I'm in for a real interesting troubleshooting project.  Yes, I have a shop manual with wiring diagram. At first everything was pointing too bad grounds then I heard or read about positive ground and everything become confusing 

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On 6/15/2018 at 8:29 PM, Dave72dt said:

Tail lights and brake lights typically use a dual filament bulb, the dimmer used for the tail and the brighter filament for the brakes AND turn signals  Brakes and turn go through the turn signal switch so you may want to check it and the brake switch itself.   Some electrical parts are designed to function correctly only when matched to their specific polarity needs.  Apparently you can smoke one of those radios designed as pos ground by reversing the polarity to neg ground.   An item like the voltage reg can be had in pos ground or neg ground and some either way, and in 6 or 12 v.  Those old regs usually had the ground preference stamped on them or if you have a part number, specs can be found that will tell you., new ones seem to be stamped with a stencil.  here again, part numbers can help.  They should also be matched to the gen so grab that number as well.  Delco controlled their gens differently than other makes of gens and as a result polarizing them was different.

Thanks for feedback very helpful

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Don,

   I trust your expertise—please make no mistake about that. However, could you please explain how a positive and a negative ground can be run together??? I’m certainly no electrical expert, and the only difference I can see in the example you presented is the voltage of each system, ie: 12v (neg) and 6v (pos). What am I overlooking? Many thanks in advance to you!!!

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From the other Don:  You can have two complete circuits, 6 volt and 12 volt, with a common ground.  If the 6 volts are positive ground and the 12 volts are negative ground, you don't want to have the live ends get together, or you will have 18 volts. 

 

Similar to house wiring, where you have 220 volts for the range and dryer but separate 110 volts circuits elsewhere.  The wonders of electrical engineering. 

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1 hour ago, DrDoctor said:

Don,

 

   I trust your expertise—please make no mistake about that. However, could you please explain how a positive and a negative ground can be run together??? I’m certainly no electrical expert, and the only difference I can see in the example you presented is the voltage of each system, ie: 12v (neg) and 6v (pos). What am I overlooking? Many thanks in advance to you!!!

 

 

As I said the circuit on a DC system must be a complete loop from a battery pole to the opposite pole of the same battery in a parallel circuit. Then and only then can voltage be present and measured. 

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On 6/16/2018 at 7:27 AM, Andydodge said:

US cars when they were 6 volt were Positive Earth......when they went to 12 Volts they changed to Negative Earth..........as for the non  working lights I'd be checking the light switch as all lights should take their power from that switch.........do you have a workshop manual with the wiring diagram?..........as your car is 6Volt then it SHOULD be positive earth.......I'd be starting over from scratch, checking the generator, regulator & starter, they should have their voltage on them..........the actual headlight switch, dimmer switch and amp gauge don't care whether they work on 6 or 12 volts, the original Fuel Gauge will need a voltage drop or resistor wired into its power circuit if the cars 12 volt..........all the globes should be the same voltage as the battery voltage............then go thru all the earth connections, check any fuses that have been added, generally speaking these mopars usually only have one fuse in a holder attached to the headlight switch and when it blows All lights are affected but who knows whether someones added a couple of extra fuses.......thats why the wiring diagram comparision to whats actually there is worth doing..............lol.......welcome aboard from Oz BTW...........lol.......andyd.      

I did a lot of mechanical work in the 60s/early 70s.  It was kind of weird, as Chrysler corp cars followed the way you described, 6v, pos grd, 12v neg.  But in the GM line, Buick 6v were + grd while Chevy was Negative and GMC trucks, near identical in appearance were Positive.  as were

 

As Don stated, it really makes no difference until there is a completed circuit.  One pole to grd, one to the component being powered.  everyone like the electricity to water analogy.  Doesn't make any difference which way water flows in a hose or a wire.

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Don Smith,

   Thank you for the clarification. So, as long as the ground wires are connecting to the common body—all is good, just don’t allow the actual ground wires to contact one another.  I’ve learned something today. And who says you can’t teach an old doc something new???

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The ground wires can touch, since they are both grounded.  Keep the "live" wires apart. 

 

For a while, I ran a 12-volt fan from two 6-volt batteries, one positive ground, one negative.  I got 12 volts betwen the two "live " wires.  And I kept the fan circuit isolated from any grounds.  I also installed a 12-volt power outlet, and could plug 12-volt accessories, including a hand-held spotlight.  But I had to wrap the spotlight shell, since it was grounded.  Touch metal, and I would get a 6-volt spark. 

 

(Later, I got a 6-volt fan, eliminated the 12-volt fan and second battery, and installed an inverter to provide 12 volts for garmins and cell phones.) 

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