pardon my ignorance

Mark W. · Mar 1, 2010

What is the difference between a positive ground and a negative ground? I am putting an electronic ignition on my super a and not sure which I need as they are either pos. or neg. ground systems.

Bob · Mar 1, 2010

(-) battery post connected to tractor/vehicle chassis = negative ground.

(Pretty much ALL new tractors and vehicles were set up like this.)

(+) battery post connected to tractor/vehicle chassis = positive ground.

(MANY older tractors and vehicles were set up like this.)

Mark W. · Mar 1, 2010

Does it really make a difference which way you do it? I was just going to use a grounding strap from the chassis to the neg. post and a cable from the pos. post to the starter.

JMOR · Mar 1, 2010

(quoted from post at 11:06:08 03/01/10) What is the difference between a positive ground and a negative ground? I am putting an electronic ignition on my super a and not sure which I need as they are either pos. or neg. ground systems.

Agree with Bob, and add that since you said on the other forum that you were also converting to 12 volts, that almost all alternators will require that you run negative ground, then you need to take same into consideration. Positive ground alternators can be had, but are rare.. Then of course, you may be planning on a generator, which can be either POS or NEG ground simply via polarizing accordingly.

Mark W. · Mar 1, 2010

Thank you both!

old · Mar 1, 2010

On any thing that uses solid state components yes how you ground will do one of 2 things. If you ground wrong you will let the smoke out. I.E. destroy the part. Now days 99% of electronic stuff has to be - ground and the moment you hook up the battery wrong you will smoke test it. As an example if you have a GM type alternator wired up if you hook up the battery + ground the alternator will smoke the moment you hook up the last cable and you can not pull a cable off fast enough to stop the smoke from escaping

Bob · Mar 1, 2010

Mark...

If you go to (-) ground (with the appropriate alternator and EI unit) for the most effective spark, connect the power wire from the ignition switch to the (+) terminal on the ignition coil.

If going to EI (likely Pertronix) be sure to use a coil with the appropriate primary resistance OR add a ballast resistor as needed.

Follow EI manufacturer's instructions as to what the minimum primary resistance their unit will tolerate.

LOW coil primary resistance GENERALLY = HOTTER spark AND more primary current and (HEATING) of the EI unit and there are limits of what they will tolerate.

Be especially careful not to leave the ignition switch on without the engine running or you may let all the smoke out of the EI unit and possibly the coil.

Jerry/MT · Mar 1, 2010

Most electronic ignitions will require a negative ground elctrical systems. There are exceptions,however.Pertronix makes some that are positive ground.

oj · Mar 1, 2010

Old, you must have had the same teacher i did for electrical stuff, my teacher told me, think of it as a water system, but with smoke instead of water, you don"t get wet , but it sure smells bad!

John T · Mar 1, 2010

All two cyliner Deeres attached the batterys POSITIVE to frame i.e. Positive ground. Many other older 6 volt tractors likweise used Positive ground while many switched to Neg ground (batterys - to frame) when they went to 12 volt.

Solid state devices like elec ignition and alternators are polarity sensitive so be sure and get an elec switch suitable for your ground because if not you will fry it !!!!!!

John T

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