Negative Ground

[rereaves]

I'm sure this has been discussed before however I'm new to group and could not find search. 

I recently acquired a 48 Dodge Coupe. The car currently has NEGATIVE ground. I have read that it should have POSITIVE ground. Should I change it? What impact does it have when car has negative vs. Positive. Currently engine runs, headlights do not work, taillights do work.

[Wiggo]

6V battery or 12V?

[DrDoctor]

Rereaves,

   Our car is a 6v/neg ground (it was that way when we acquired it), and everything works just fine, with the obvious exception of the radio. Since it grounds thru the case, when it was reconnected, the tubes fried, and we now have a rather large worthless burnt lump. If you change the car back to positive ground, I think you’ll have to re-polarize the generator. I don’t know about the starter, or the voltage regulator, as I’ve heard conflicting advice. If you’re converting to 12v, it’ll be negative ground, and you’ll have to deal with the voltage change, with the polarity change being a moot point in such a conversion. if you're keeping the car a 6v, I’m VERY interested as to how you proceed with this. Best regards . . . . .

Edited June 16, 2018 by DrDoctor

[garbagestate 44]

You might want to poke around a bit to try and figure out why the previous owner changed it in the first place.

[Wiggo]

3 hours ago, DrDoctor said:

Wiggo,

   Our car is a 6v/neg ground (it was that way when we acquired it), and everything works just fine, with the obvious exception of the radio. Since it grounds thru the case, when it was reconnected, the tubes fried, and we now have a rather large worthless burnt lump. If you change the car back to positive ground, I think you’ll have to re-polarize the generator. I don’t know about the starter, or the voltage regulator, as I’ve heard conflicting advice. If you’re converting to 12v, it’ll be negative ground, and you’ll have to deal with the voltage change, with the polarity change being a moot point in such a conversion. if you're keeping the car a 6v, I’m VERY interested as to how you proceed with this. Best regards . . . . .

Doc, my car is already 12v negative earth. If someone has a neg earth and problems as described (i.e. random) the starting point has to be to figure out what the previous owner has done. I could have been facetious and said if the OP swaps back from neg to pos ground, his headlights will work, his tail lights won't and his engine will run back to front, but that wouldn't be that helpful.

 

 So, my question is: is the car 12v neg ground or some horrid hybrid 6v neg ground?

[Dave72dt]

Other than a couple of polarity sensitive components like the voltage reg and radio, ign coil and amp gauge maybe the fuel gauge/sending unit, positive or negative ground doesn't really matter as long as all the electrical components match the polarity.  Coil and amp gauge wires reversed, generator repolarized are the main issues and those things may already have been done.  It's not that uncommon to find recent acquisition hooked up as neg ground since that's what most people are familiar with.

[busycoupe]

As to your headlight problem, it may just be a dirty high beam switch.  Stomp on the switch several times. They are supposed to be self cleaning with use.  If that does not help, I would check the bulbs.  It is very possible that both are burned out.  If someone changed the car  to 12 volts and did not change the bulbs, the 6 volt bulbs wouldn’t last long.  

[rereaves]

On ‎6‎/‎14‎/‎2018 at 12:45 PM, Wiggo said:

6V battery or 12V?

6V Battery

[rereaves]

The Battery is 6 Volt

[rereaves]

21 hours ago, busycoupe said:

As to your headlight problem, it may just be a dirty high beam switch.  Stomp on the switch several times. They are supposed to be self cleaning with use.  If that does not help, I would check the bulbs.  It is very possible that both are burned out.  If someone changed the car  to 12 volts and did not change the bulbs, the 6 volt bulbs wouldn’t last long.  

 

[rereaves]

On ‎6‎/‎14‎/‎2018 at 3:05 PM, DrDoctor said:

Wiggo,

   Our car is a 6v/neg ground (it was that way when we acquired it), and everything works just fine, with the obvious exception of the radio. Since it grounds thru the case, when it was reconnected, the tubes fried, and we now have a rather large worthless burnt lump. If you change the car back to positive ground, I think you’ll have to re-polarize the generator. I don’t know about the starter, or the voltage regulator, as I’ve heard conflicting advice. If you’re converting to 12v, it’ll be negative ground, and you’ll have to deal with the voltage change, with the polarity change being a moot point in such a conversion. if you're keeping the car a 6v, I’m VERY interested as to how you proceed with this. Best regards . . . . .

Thanks I will work on dimmer switch to see if that helps

[rereaves]

Thanks for the feedback, I think I'm going to leave it neg ground.  The car starts fine and most of the electrical items seem to work, less radio and headlights.  

[rereaves]

22 hours ago, Dave72dt said:

Other than a couple of polarity sensitive components like the voltage reg and radio, ign coil and amp gauge maybe the fuel gauge/sending unit, positive or negative ground doesn't really matter as long as all the electrical components match the polarity.  Coil and amp gauge wires reversed, generator repolarized are the main issues and those things may already have been done.  It's not that uncommon to find recent acquisition hooked up as neg ground since that's what most people are familiar with.

 

[rereaves]

I recently installed a new battery, coil, points and condenser along with new plug wires.  Since I did not know about positive ground, I simply installed the coil and placed the wires in the same location.  I can't remember what coil post and wire I used but it seems to work.  The Amp meter is stable even during acceleration, no needle swings.  The gas gage is another issue it bounces all over the place.  Heater fan motor works, however dash lights do not work.  Brake lights do not work but tail lights work. Head lights do not work, along with turn signals.  I'm assuming that I have a ground problem but not sure since this car is new to me.  

[rereaves]

22 hours ago, Dave72dt said:

Other than a couple of polarity sensitive components like the voltage reg and radio, ign coil and amp gauge maybe the fuel gauge/sending unit, positive or negative ground doesn't really matter as long as all the electrical components match the polarity.  Coil and amp gauge wires reversed, generator repolarized are the main issues and those things may already have been done.  It's not that uncommon to find recent acquisition hooked up as neg ground since that's what most people are familiar with.

 

[rereaves]

This is what I have done, not knowing the issue with positive ground.  The car is 6 volt neg ground.  I installed a new battery, coil, points, condenser, plug wires and plugs.  The car seems to start fine however the battery has a hard time cranking over the motor.  I assume this is typical 6 volt issue.  Taillights work, no brake lights.  Headlights do not work and no turn signals.  Amp meter is stable, heater fan works, fuel gage is all over the place, oil pressure is around 40, radio does not work.  

 

My first thought is a ground problem however I do not understand positive ground impact on those items not working.  

[rereaves]

22 hours ago, busycoupe said:

As to your headlight problem, it may just be a dirty high beam switch.  Stomp on the switch several times. They are supposed to be self cleaning with use.  If that does not help, I would check the bulbs.  It is very possible that both are burned out.  If someone changed the car  to 12 volts and did not change the bulbs, the 6 volt bulbs wouldn’t last long.  

 

[rereaves]

Thanks I will stomp the hell out of it tomorrow.

[Dave72dt]

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.

[rereaves]

11 hours ago, 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.

 

[rereaves]

Thanks again for the info on the electrical system.  I will follow through on your suggested possible causes for headlight and brake light issues.  I just can not get my head around a positive ground system.  All I can think of is attaching the positive battery cable to the motor and creating one large welding machine.  I now realize after doing some reading and asking that 6 volt positive ground was more common than I thought.  Just how do you attach the positive battery cable to ground without creating a large spark?  I'm planning on purchasing new larger wire size battery cables, looks like what's on the car is 12 volt cables.  I'm also wondering if someone started to convert to 12 volt but never finished.  The Gen, Starter and Voltage Reg look like OEM equipment.  Like I mention in one of my reply's I changed the coil.  I just went to NAPA and told them I wanted a 6volt coil for 48 Dodge.  I simply wired the same way as old coil.  The old coil case was split open by what I assume was clamp pressure. The battery I purchased is not what I want, the Cranking Amps are around 750 and the physical size of the battery is too small for the battery tray.  I think I have found a local source but have not checked it out. I will also start searching part numbers for things like the starter, gen and other electrical components as you suggested.  Can you tell me the physical location of brake switch.  I can not find anything near the brake pedal or master cylinder?  My shop manual does not show a picture or discuss that I can find.  

 

Thanks Again

[Andydodge]

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.      

Edited June 16, 2018 by Andydodge

[DrDoctor]

Rereaves,

   As I mentioned earlier, our car’s 6v/neg ground when we got it. Exception of the radio, things worked fine when we got it, and still do. The insulation throughout the car was extremely brittle, and falling off of the wiring, so I rewired it using a Ron Francis Wire Works “Git It Runnin’” harness, leaving it 6v neg, and have had no problems since that project. I installed 6v quartz halogen headlights, and that made a terrific difference. I installed turn signals, and wired the tail lights to illuminate along with the trunk light. I had to reverse the wires on the ammeter, since the polarity’s reversed. I’ve heard a lot of comment re: wire gauge when using a 12v harness in a 6v car. The “Git It Runnin’” harness from Ron Francis Wire Works has that issue addresses, and in the several years since the rewiring’s been completed, not one problem encountered. Having done all of this, would I change the polarity back to positive? NOPE—can’t imagine a reason why I should even consider it. Just my thot's on this. Warmest regards . . . . .

[Don Coatney]

On any DC circuit the loop must be complete to both battery poles for anything to function irrelevant of ground polarity. It is possible to have a dual voltage automobile as pictured below with both a 6 volt positive ground generator and a 12 volt negative ground alternator both systems sharing a common ground.    

 

 

[50net]

look on rearend for brake switch