12V wiring problem

bmace · Post by **bmace** » Mon May 30, 2016 8:01 pm

I have installed an alternator (1-wire) on a JD 420C. The tractor is wired for Neg grnd.The 12 V coil is new and requires an external resistor.My question is ,does the resistor go in line between the coil and distributor or is it okay to install inalternator to battery line?

shinnery · Post by **shinnery** » Tue May 31, 2016 12:37 am

The external resistor is to reduce the current thru the coil and points. The normal place for it is between the coil and battery but it can be anywhere as long as it is in series with the coil and points as one side of the points is grounded. The complete circuit (assuming negative ground because of alternator) is normally Positive post of battery, switch, ext res, positive terminal of coil, negative terminal of coil, points, ground, negative post of battery. The ext resistor will work on either side of coil.
Bryce

shugy368 · Post by **shugy368** » Wed Jun 01, 2016 7:57 am

As owner of a JD420-C with positive ground did someone change the polarity wiring for your tractor and was that done just to get an alternator set up vs gen?

Stan Disbrow · Post by **Stan Disbrow** » Wed Jun 01, 2016 9:45 am

Hi,

The polarity matters only to the battery, generator and regulator. Once the 6v pos gnd is cut loose and a 12v neg gnd alternator, with either internal or external regulator is put on, the polarity swap is complete. Hook the new 12v batt up neg gnd and go.

One still has a 6v coil, and so that needs a ballast resistor in line with it or it will fry. From voltage, not polarity.

The real risk is to the 6v starter if that remains. It won't fry much if you limit crank time to two seconds or less. But, it might over torque the nose cone, and those are NLA..... Not to mention beat up the ring gear.

Personally, I do not do this. I keep them original.

Stan

bmace · Post by **bmace** » Wed Jun 01, 2016 5:44 pm

Thanks for all the feedback on the 12V problem.I did have it wired correctly with the resistor in the right location. The problem was the machine was backfiring and acting like a possible wiring problem I might have created when I rewired . Eventually,fter a long process of elimination,I located the problem as being the condenser in the distributor. Changed it out and everything seems fine for now.

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