Posted by John T on November 10, 2010 at 05:48:34 from (66.244.97.31):
In Reply to: Poor spark posted by best785 on November 09, 2010 at 22:28:24:
You ask "Do you need a resistor" heres the answer assuming its a 12 volt tractor.
Iffffffff its a 6 volt coil YES you need an external series voltage dropping (12 to 6) ballast resistor or else it will get very very hot and the points will burn up prematurely.
Ifffffffff its a coil designed for use at nominal 12 volts DO NOT USE AN EXTERNAL BALLAST or the spark will be weak. Some folks call those "internally ballasted"
Iffffffff the coil is labeled "12 volts" or "12 volts NOT for use with ballast" or "12 volts NO ballast required" its designed for use on a 12 volt tractor with no ballast resistor.
Ifffffffff the coil is labeled "12 volts requires ballast" its more in reality like a 6 volt coil and indeed needs the ballast or it will overheat.
"Many" coils designed for use on 6 volt tractors have a primary reisistance between the + and - terminals of around 1.25 to under 2 ohms....."Many" coils designed for use on 12 volts tractors with no ballast have a primary resistance in the 2.5 to 3.5 ohms range. Thats so the points dont have to switch too much over 4 amps or else they burn up too fast.
If the spark is weak I suspect points or gap then next a bad condensor while a bad coil is way down the list. Wire the coil to match polarity as posted below i.e for Neg ground the coils - wires to distributor
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