Positive verses Negative ground ?

[Guest BudaHotRod]

While I'm trouble shooting my flathead 6 problem I discovered that the way my battery is set up, common sense would tell me that it is a positive ground. Positive side is bolted the the head and the negative goes to the solenoid. I was told the car was a negative ground. Can some one explain the differences. I have an unmolested stock 331 Hemi from a 55 Chrysler New Yorker (still in the New Yorker) that is supposedly a positive ground 6 volt. I am considering fputting it into my 1950 Plymouth. Any body have any inputs or advise on this engine swap ?

BudaHotRod

[bob westphal]

A lot of the older cars had a positive ground. Like Packard, Ford, Mercury, Lincoln, and all MoPar's, if I remember correctly, until they went to 12volt. The difference is the polarity on the amp gauge and the battery cable hook up. Everything else would be the same as negative ground. Unless someone switched the polarity on your car it is postive ground. There are some guys on the forum that have info on the engine swap. It's been done a lot.

[Guest jjmorrse]

I know they were + ground as far as I know. A lot of times, people will have switched them over the years. My 54 was switched when I got it. The amp gauge will read either way, but just opposite. To go to - ground, you need to switch wires to the coil, the ammeter (if you care if it reads right), and the battery posts. After a lot of generator, regulator problems, I switched to 12 volt with a flatback alternator and a electronic regulator, but 6 works fine if you remain on top of it

[grey beard]

Can anyone tell me WJY most auto makers used to use Positive ground polarity on electrical charging systems? Here's a hint - many big truck makers still do this, and there's a really good reason for it that most people never heard about.

Let's see who knows their stuff about electricity. LOL:D

[1just4don]

Here is what I learned over the years. IF its a positive ground the positive side of the coil will go to the distributor. IF the negative terminal of the coil is hooked up to dist. then somebody switched it over OR made a bad mistake exchanging coils etc. They dont run quite right polarity reversed, but sometimes runs. Sometimes NOT. It is an easy quick check to see if things are okay.

[Plymouthy Adams]

even quicker..hook it up battery, engine off, pull on the lights..look at amp meter..

[Tim Frank]

Galvanic corrosion

[55 Fargo]

I believe Mopar switched to all 12 volt in around 1955 to 1956 sometime, but if you have a 6 Volt positive ground, the polarity is opposite of a negative ground, the lights, wipers, heater motor, starter could care a less if the polarity is switched, but a radio does require the same polarity. In fact a 6 v starter should be fine if switched to 12 v negative, it will also spin faster. You would require voltage reducers for your heater motor, horn, wipers. Do you plan on using a 3 spd standard or a semi-auto trans with fluid drive, as that would also require some voltage reduction for it's electrical mechanisms. As also mentioned your amp gauge would have been reversed if changed from positive to negative ground other wise it would indicate discharge whan actually charging. Good luck...........Fred

[rearview]

I've been keeping my eye on this since I got mine and it's set up for negative ground. I'll give the ammeter a look after work, but the thing that puzzles me is why the heater blower motor is blowing the right way, unless somebody flipped it around.

Bob

[55 Fargo]

Thats always a possibility, but funny thing my starter when I got my car was wired some kinda weird 12 v conversion,it's now back to 6 volt positive ground the starter, spins in the right direction regardless of the polarity. But not sure about a heater motor.............Fred

[greg g]

starter motors and generators are polarity neutral until the field coil is energized. Since the field coil is a temproary magnet, not a permanent one, the starter motor always spins the same way. Also a 6 V starter is much more robustly built than a 12 V and will usually stand up to 12V use for a long time.

To the other question, electricity flows naturally fromthe negative to the positive, thats why positive grounding was used.

[Young Ed]

And apparently the mopar heater motors are wired the same was as a starter. Mine spins the same way regardless of which wire is hooked up to what. Thats why I'm still lacking a drivers side motor.

[martybose]

(snip) ... the lights, wipers, heater motor, starter could care less if the polarity is switched, but a radio does require the same polarity.

This comment about the radio isn't necessarily true. If it is an all original radio, like the 802 that I have, it will work just fine on 6V negative ground. I was told that the OEM vibrator didn't care about polarity, but an upgraded electronic vibrator would. So my radio was unaffected when I changed from a 6V positive generator to a 6V negative alternator.

Marty

[grey beard]

Whoever it was who said "galvanic corrosion" was on the mark. Truck manufacturers have learned that when a vehicle moves on winter roads it is often inveloped in a spray of salt water from all the stuff spread on the roads in cold weather. The thinking is that since electrons flow from negative to positive, a positive ground will aid in preventing rust and corrosion. In the eighties we had an entire fleet of Western Star trucks with 12 volt positive ground, just for this reason.

You are nearly all right in what you say about polarity. Heater motors and starter motors are not polariy sensitive. Ignition systems ARE polarity sensitive and should be connected properly whether they are six or twelve volts. Again, since electrons flow toward the positive, we want a positive ground at the spark plug on the secondary side, so the secondary voltage will jump the gap from the center insulator to the grounded threads on the cylinder head. Thus the head is positive (ground) while the voltage leving the coil and distributor cap should be negative. When a coil is connected backwards the spark travels through the engine block and returns thru the spark plug to the distributor - definitely not good, cause it takies more voltage to jump the same spark gap at the plug.

This is all true because voltage will more readily jump from a colder surface to a hotter one. Reversing the coil's polarity will reverse the flow of secondary voltage. All this has nothing whatsoever to do with charging system polarity. They are related only in that when charging system polarity is changed it also changes coil polarity - unless the electrician on the job knows shis stuff and corrects for it. Plain as mud, right?