no spark

12 volt conversion complete ...now no spark new plugs, points and condenser,distributor cap. Do I need 12 volt coil ???

I would use a 12 volt coil but, you can get by with an inline resistor of some sort. Did you use a conversion kit, some of them come with a resistor in them. On another note, I would have thought you'd have spark even without the resistor for a while...hope the points aren't burnt.

12V conversion on what? Is there voltage at the coil on the ignition switch side? Are the points completing a path to chassis/ground. What is the actual primary coil resistance on xoil's primary windings.

Farmall c

There are 2 kinds of "12 volt coils". One is marked "12 volts, external resistor required". It has 1 1/2 ohms across + - terminals which is equivalent to a 6 volt coil. An equal value 1 1/2 ohm resistor is required.

Other type is "12 Volt, No external resistor required". It has 3 ohms across + and -, and does not require a resistor.

I have seen some conversion kits that include a resister with too high an ohm value which will cause hard starting and perhaps low power. You can check it with an ohm meter or by bypassing the resistor for a short time.

If you are using the original coil check for rust in the large center terminal or a bulging case. If it has either I would replace it. I'd use the "no resistor required coil" and eliminate the resistor. Use NAPA IC14SB coil or equivalent.

Where is the voltage and current on the Farmall C ?

That is an over simplification. G.M., Ford and Chrysler used different coils and different resistors to match on 12 volt cars. A Chrysler resistor on a G.M. coil will burn points while a G.M. resistor on a Chrysler coil will have weak spark. 12 volt coils without resistors on American cars are EXTREMELY rare. They were used on John Deere A and the first Deere number series tractors along with some other brands as well as old Deere combines.

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

Copy and paste into your browsers URL address

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T Retired Electrical Engineer
John Ts Ignition Troubleshooting