Posted by John T on July 31, 2017 at 13:41:23 from (216.249.81.101):
In Reply to: no spark posted by newhaven on July 31, 2017 at 04:43:17:
On that 12 volt tractor you can use EITHER:
a) A full 12 volt rated coil no ballast required. It may be labeled "12 Volts" OR "12 Volts not for use with ballast resistor" They are readily available at NAPA or Tractor Supply or Rural King. It will have a Low Voltage LV primary resistance of around 2.5 to 3.5 or so ohms (many are 3 ohms).
b) A 6 Volt rated coil PLUS an external series voltage dropping (12 down to 6) ballast resistor. It will have a LV primary resistance of around 1.2 to 1.8 ohms (many are 1.5 ohms). Many typical common old tractor ballast resistors are around 1.2 to 1.8 ohms SUBJECT TO the LV primary resistance of the coil they are used with. If its a 12 volt tractor and you use a 6 volt coil in order to get a 50 50 voltage divider so 6 volts are dropped across the resistor leaving 6 volts for a 6 volt rated coil, the coils LV primary resistance and the ballast resistance is close to the same IE 1.2 to 1.8 or so ohms each.
NOTE since this is an old farm tractor forum and NOT an old car forum, I'm talking about typical old farm tractor 6 and 12 volt coils and the ballast resistors they used. Still FYI some 12 volt US made cars and trucks used 12 volt coils while some used 6 volt coils plus an external ballast resistor.
I would use a full 12 volt rated coil no ballast required for simpler wiring. Many old farm tractors that were 12 volt still used a 6 volt coil PLUS an external ballast PLUS a start ballast by pass system to improve cold weather starting.
NOW if theres no fire if you work through my Ignition Troubleshooting procedure it can help find the cause. Its simple and easy step by step and no fancy tools are required
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