Ignition update/upgrade--6volt neg ground?

Mon Sep 27, 2004 8:56 am

I just purchased a '51 Cub and I am having a lot of fun with it and I 'm getting some chores done, also! I want to fix it up to get good preformance and the best reliability I can.

I am working on the electrical system first. But I first noticed the electrical sytem is 6 volt negative ground. What is going on? The Manual
said it is a 6 volt positive ground system. Is there some type of conversion?

I would like to install the new solid state ignition system and a 12 volt neg ground stystem. What should I do for maximum preformance and relaibilty? Where should I buy these parts, how much should they cost? Are they fairly easy to install?


Mon Sep 27, 2004 9:18 am

The original system was 6 volt positive ground. Many times over the years they get switched to negative ground by someone changing the battery and not realizing that the original was positive ground because they have never seen or worked on anything but 12 volt negative ground systems. Sometimes the change was intentional because people thought all grounds should be negative. Only minor wiring changes were necessary to make the change. The 6 volt system works equally well either way.
That being said, a well maintained 6 volt system will do all that is required. There are 6 volt positive ground electronic ignition systems available from Pertronix and probably other vendors. There are 12 volt systems available also. So, the choice is yours.

Mon Sep 27, 2004 9:28 am

Thank you. Is there much invloved to change my sytem to 12 volt? I have heard it said that after changing to 12 volt the starter/gen. will crank the engine over faster, and my Cub would like that when starting.

Mon Sep 27, 2004 9:40 am

mmann check this out it may help

Mon Sep 27, 2004 9:40 am

Assuming that you use an alternator, the only other thing you would have to change would be the lights. The starter will work fine on 12 volts. As far as your 6 volt starter turning slow, check your battery cables and connections including the grounds. I re-wired mine with 1/0 welding cable and all new ends with clean, shiny connections and it cranks like a 12 volt system. Over the years, most ground cables get replaced with smaller gauge 12 volt cables and they cannot carry the current load required for the system to function properly. Therefore, the resistance from any corroded connections is significant because the cables heat up quickly. The tractor will work fine on 6 volts if you maintain it and it will be much cheaper than a conversion.

Mon Sep 27, 2004 10:08 am

After reviewing the replies, I think my best course of action is leave my cub at 6 volts, negative ground. Big Dog makes a good point with the smaller cabes not doing the job. I will replace both cables and put on new ends. Recharge battery. Tighten belt for generator to spec in operator's manual. Then all I need to do is find a solid state ignition sytem for 6 volt negative ground.

Am I on the right track?

Huge thanks!

Mon Sep 27, 2004 10:27 am

Go ahead and switch it back to positive ground. All you will need to do is to switch the leads on the ammeter and re-polarize the generator.

Hey Bigdog.....Please en"light"en me....

Mon Sep 27, 2004 10:47 am

I'm interested in this topic, as I'm like a lot of others in that I'm accustomed to the 12 volt negative ground systems. My cub ~ 1950 does have the 6 v positive ground. Apparently something is starting to drain the battery as even with driving the cub around mowing an acre, the battery seems to be draining. The battery is new, and I've been told the starter has been rebuilt, so has the generator, and the regulator has been replaced. However, I can easily see wires with little or no insulation on them. I recently put the battery on charge with the positive cable on the positive post of the battery, and the negative cable on the negative post of the battery. When I first started the charge (trickle) the charger needle dropped to right at 5 volts, then gradually back up to a little over 5 volts. I charged the battery for about an hour and a half. I haven't yet tried to start the tractor because I wanted to ask about the charge. Right now, I have the positive cable on the battery disconnected. Did I charge the battery correctly, and am I safe in trying to reconnect the cable and do a test startup?

Thanks for the tips and help.


Mon Sep 27, 2004 11:24 am

Yes, Battery chargers are always connected according to battery polarity. They do not care which post is ground, only that they are connected plus to plus, negative to negative. You may need to polarize your system as your tractor may be trying to charge the battery backwards.

Thanks Bigdog....

Mon Sep 27, 2004 12:40 pm

I'll give it a try this coming weekend. Hopefully Jeanne will be long gone by then, and I can uncover the cub and see if it will start. I'm going to at least tape the bare wires and see if that helps. Maybe this winter I can get the brakes, radiator and wiring done so the cub does better than it does now. BTW, I really enjoyed your cubarama photos.


Mon Sep 27, 2004 1:03 pm

So all I have to do to bring back to spec is
1) get bigger cables
2) ground the positive lead
3) negative to the starter switch
4) polarize the system by quickly jumping the batt terminal with the gen
terminal on the voltage regulator.
5) relax, this is a hobby.


Mon Sep 27, 2004 1:18 pm

Now yer talkin'! :) :) :)

Mon Sep 27, 2004 1:33 pm

I have to say, this forum is going to be a huge help to me. I plan to work on the mechanics thru the fall and winter and then next spring, paint and decals!

I was driving west on Interstate 70 in Indiana last Thursday morning. I saw three differsent trucks pulling trailers with Cubs on them, heading west between Indianapolis and Terra Haute. I knew something was going on somewhere and I was missing it. Got home and got on this website and found it was CUBARAMA!!

After seeing Big Dog's Pics....I will be there next year.


Mon Sep 27, 2004 1:38 pm

Where in Kentuck are you from? (not to be nosey but my wife's family is scattered over Kentucky and southern Indiana.)

Mon Sep 27, 2004 1:57 pm

Think nothing of it. I live near Lousiville, KY. in Prospect. I have 20 acre playground near New Castle, KY. where my Cub works and me and my two sons play. The Cub mows, and plants food plots for feeding deer. During the week I travel all over KY. and IN. as a salesman. My great grandfather was a traveling salesman, also, but he worked for International Harvester.