Converting to negotiate ground

Ok I know this has been discussed a million times but I have to rewire my d15 which has gone through a few ignition kits. It is 12 volt positive ground. But between it and my d17 I need an alternator anyway so I was wondering about switching to negotiate ground. It is my understanding that I can use the same starter when I switch is that correct or do I need to replace the starter? It actually has a new starter so I don't want to replace that.
I am a little confused by this because I thought polarity determined the direction of rotation for these dc motors. I am thinking of an electric train set I had as a kid it had a -15 to 15 volt dc power supply and when you put negative 15 volts it was full speed reverse positive was full speed forward.   So while I have read a bout people swapping the systems and keeping the starter I am confused.

Edited by Dan73 - 01 Mar 2016 at 2:55pm

You can use the same starter , IT doesn't have to be rewired for negative ground. 'They' designed them so they spin the RIGHT way regardless of batter polarity.
The best thing to do is to 100% rewire the tractor ! Eeither get a kit from Steve@B&B or 'roll your own'. There's only maybe a dozen wires and NO computer!! Please do NOT use ANY of the 50+ year old wiring. I put the alternator 'idiot' light in a preexisting 1/2" hole in the lower left of the D-14 dash.

Jay

thendrix wrote: So how does negotiate ground work? Sorry couldn't help it. Besides I've called the wife the wide on several occasions. Once in a text to her. That was a fun explanation. I guess it just happens sometimes.

Maybe that is why I lost two pertronix kits... The funny part is I read right over it when I did go back and fix a couple of the auto correct errors.

Thanks guys for the feedback. I think this one might get swapped.

JimD wrote: The starter will be fine.  Swap battery terminals, coil leads, and add the alternator.  Lots of good wiring kits out there, and some real junk.

Do not even need to add an alternator.  The old generators still do the job well.  One other thing to do is switch the terminals on back of the ammeter.  Very easy to do.  Did it on all of my tractors.  Also agree with a new wiring harness. 

I don't see why there would be a problem with the Pos. ground unit vs the Negative ground unit other than being installed incorrectly or spiking the system accidently with a booster charger. We sell a boat load of the 12VPG as well as its Neg Grd cousin. If you decide to go to an Alternator, you would need to go to Neg. ground anyway. Paul's statement is quite true. The E.I. that's in my 6V B is now going on 17 years old. I only just put a Distributor cap on it last year or so. The only reason why I did that is because its been sitting outside tarped over most of those years in between me using it frequently, and the moisture eventually gets in the caps and starts corrosion around the high tension towers. To elude a possible problem, I treated the ole' girl to a new Distributor cap. We offer 12V conversion kits, and also an "SI" Alternator retrofit kit for the "D" series Tractors as an update from either the Gennie or the "DN" series Delco external regulated Alternator. If you visit our website you see some pics on the kits. If the kits are out of your budget, we can help with parts, pieces, and lottsa' info to help you out and walk you through any problems or questions you may have. That doesn't cost ya a dime. There is a lot of information I put on our site for folks to read and learn about the do's n' dont's of electrical systems. There's also a "how to" on the installation of Pertronix E.I.'s.   HTH
Steve@B&B

So long as the charging polarity is observed and the battery always connected to match (guided by the relative sizes of the battery posts) either polarity works for starting, ignition, lights, gauges, and charging. Ignition coils with points and ammeters are somewhat sensitive to polarity, coils giving better spark when properly connected and ammeters giving correct charge or discharge indication when connected properly. Some gas gauges are sensitive to polarity. They don't destruct, they just don't read right.

The SAE (Society of Automotive Engineers) standard on vehicular electric system until some time in the 1950s allowed either polarity and 6, 12, or 24 volts. For several decades before that automotive electrical engineers argued over polarity, primarily based on corrosion of ground connections to the frame. Neither side had a winning argument but polarity varied by manufacturer. The mid 50's revision of that SAE standard dropped 6 volts, and the early 60's version dropped positive ground, and stiffened the requirements for 24 volts making that voltage less desirable. I believe the development of solid state radios and accessories drove the change, but consumer safety and simplicity surely was a factor. Tube car radio with a vibrator power supply worked the same with either polarity if they used a rectifier tube for the high voltage. Two way radios with a vibrator often used a more complex vibrator that did the switching and the rectification. Many were designed to fit the socket in two positions to accommodate positive and negative grounds. Radios with dynamometers required some wiring changes to switch polarity. Thing was that with reversed polarity a tube type radio just didn't work, parts weren't always damaged. With solid state radios reversed polarity caused instant blowing of transistors far faster than the blown fuse. In that transition period some transistor radios were made with switchable polarity. With the polarity sensitivity of the alternator having only one polarity in use cut the manufacturing and warehouse varieties in half though alternators have been made for positive ground but you won't find one easily and a few have been made with switchable polarity. Plus having a single polarity simplifies life and improves safety for the least experienced user replacing battery and jump starting. Even when designing circuits, it takes extra thought process to design positive ground circuits which were common in germanium transistor days. Not every engineer was good at that.

Gerald J.

I'm surprised that nobody mentioned the coil. It should be changed to a 12v coil or have a resistor in the now positive 12V feed to avoid heating (and eating) up points.