Farmall Cub

1950 Cub, battery ignition, 6 volt, positive ground.

Does it matter which terminal ( + or - ) on the ignition coil is wired to the distributor? Will it run no matter which way it is wired?

Thanks.

No it must be hooked up polarity correct.

In the case of a positive ground tractor. The minus sign is connected to the breaker points in the distributor and the plus sign is energized by the ignition switch.

lazyuniondriver wrote:No it must be hooked up polarity correct.

In the case of a positive ground tractor. The minus sign is connected to the breaker points in the distributor and the plus sign is energized by the ignition switch.

the wire from the switch should go to the neg. side of the coil on a 6 volt pos. ground, and the pos. side to the dist.
BOSS

Dave50cub wrote:1950 Cub, battery ignition, 6 volt, positive ground.

Does it matter which terminal ( + or - ) on the ignition coil is wired to the distributor? Will it run no matter which way it is wired?

Thanks.

It likely would not make a difference. In theory only, there can be a difference in ease of sparking but may not be in real life. The negative side of the sparkplug needs to be the hot, i.e. temperature, electrode but is the temperature difference enough to really affect the ability for the spark to jump the plug gap?

I have a cub with dual spark coils. One plug has a positive center electrode and the other has a negative electrode. Both need to fire or neither will fire. All or none.

They both fire even though one is the opposite polarity from the other. Also used on motorcycles and I expect those plugs are much hotter than what you may find in a cub.

I have switched back and forth and not noticed any difference. It would be interesting to try both ways and post back with the results.

Boss Hog wrote:the wire from the switch should go to the neg. side of the coil on a 6 volt pos. ground, and the pos. side to the dist.
BOSS

I hope I didn't open a can of worms here. I did not reference the manual but my 51 six volt positive ground tractor, original style IHC coil and wiring.

I was almost 100% positive you would hook the points to plus and the feed to minus but I went out and triple checked how mine is wired before I posted, which on a trip back outside for a fourth check is wired as I stated, starts and runs perfect.

A coil is marked for polarity so I have never hooked one up in reverse polarity so I can't tell you if one will work properly hooked up in reverse polarity. Did the previous owner do a switcharoo? 100% possible.

Since the connections look a little grimy, this will give me an excuse to remove the wires to clean them, switch them around and see if it starts.

I apologize for any confusion but I only have one positive ground electric ignition tractor to reference today.

no can of worms at all.

lazyuniondriver wrote:A coil is marked for polarity so I have never hooked one up in reverse polarity so I can't tell you if one will work properly hooked up in reverse polarity.

I've run across several engines with the coil hooked up the wrong way. It makes less difference than you might think. I think it is just one of those small things that, when combined with other small problems can add up to a poorly running engine.

By the way, a Cub magneto (and others with a rotating magnet) will reverse polarity with every half rotation. So 2 plugs fire negative and the other 2 fire positive. I'm not sure about the older mags with a stationary magnet. It would depend on how the commutator is designed.

Well Jim, I have just run across my first one.

My findings were firstly I found the coil mounted upside down in the clamp, secondly I found a lockwasher under the feed terminal eye indicative of someone here before me.

I cleaned and reversed the polarity and started the engine with no noticeable difference in performance. Since the manual calls for the plus to be grounded at the points as Boss Hog previously posted, I completed the assembly in that fashion.

The reason I looked before posting is because of my limited exposure to positive grounded equipment. I did not want to mislead anyone by relying on my memory.

I will have to end this post with a question since I never studied electrical engineering beyond Ohms law nor have a degree.

Why is a coil marked for polarity if it can be hooked up polarity incorrect? Is there any difference whatsoever in the coils ability to generate current when polarity is reversed?

As I stated earlier, I would never have knowingly connected a coil backwards so I never knew it was possible to do so.

The floor is open gentleman.

For what it is worth, the coil on my tractor has the negative terminal wired to the distributor. The positive terminal is wired to the switch. The tractor is running fine.

When I get a chance, I will reverse these connections to see if there is any effect on the tractor's performance, but from what others have said so far, there probably won't be much of an effect.

It might be interesting to take a survey of those reading these messages to see how the ignition coils on their tractors are wired (provided they are positive ground and 6 volt, battery ignition systems). There might be enough tractors of this type wired each way to give us a pretty good idea whether the coil polarity really makes any difference.

My reference: Automotive Diagnosis and Tune-up, Wetzel, 1969. In case you are bored, the text book has 4 pages explaining coil construction and theory.

Ignition coils are connected so that the high tension current will have a negative polarity, regardless of battery polarity.

A simple check for correct coil polarity.

Ordinary lead pencil. Engine at idle speed, insert the pencil point in the gap between the end of the ignition cable and the spark plug terminal, If the flare appears on the plug side of the pencil point, the polarity is correct, negative.

For low rpm, limited number of cylinder engines, coil polarity isn't going to make a difference. A polarity problem is more likely to show up on 6 or 8 cylinder engines at high rpms due to lowered current draw at the coil (related to the number of sparks per second) and cylinder compression.

Eugene wrote:My reference: Automotive Diagnosis and Tune-up, Wetzel, 1969. In case you are bored, the text book has 4 pages explaining coil construction and theory.

These are the text book manuals I pored through before and during college along with old technical flicks gaining the knowledge necessary to successfully compete in troubleshooting competitions.

I vaguely remember an instructor (I still remember his name) demonstrating the lead pencil test but would never have remembered that had you not jogged my memory.

Component troubleshooting technical manuals such as the one you referred to will probably never be scanned for the internet and hopefully libraries will continue to keep them on their shelves for years to come.

I surely appreciate you taking the time to dig this reference up to satisfy my curiosity.

lazyuniondriver wrote:I surely appreciate you taking the time to dig this reference up to satisfy my curiosity.

No digging necessary, the book was laying on the floor next to the desk along with a stack of other frequently used references. Less used references are maintained in three book shelves full of assorted books on mechanics, construction, building codes, history, government and any thing else that interested me from time to time.

I have to agree with Eugene, coil polarity is not going to make much difference on the typical tractor engine. Where I've seen to show up and cause issues is in automotive applications. There, it can show up as a strange misfire, that's hard to put your finger on. I haven't done the lead pencil test in years, but it will point to the problem very quickly. I have found mismarked coils that way. If I remember correctly, reversing coil polarity will also have an adverse effect on point life.