424 ignition problem

I have a 1967 IH 424. It has a keyed on/off ignition switch and a separate push button for cranking the engine when starting. The tractor starts and runs fine while pushing the start button but dies when the button is released. I can see the spark at the plugs when cranking, but there is immediately no spark when I release the starter button. Any ideas why this is? How much resistance should the ballast resistor measure? What is the purpose of the wire that runs from the coil to the starter solenoid?

The wire from the starter to the coil bypasses the ballast resistor during cranking (with the starter).

If you have a bad wire from the ignition switch to the ballast resistor or a bad (open) ballast resistor, the tractor will act just as you describe.

I can't remember the exact circuit, but don't think it will crank (with the starter) if the actual ignition switch has failed.

I don't know the exact value of the ballast resistor, but expect a reading in the 1.5 to 2.5 Ohms range.

Ted, Im NOT at all familiar with that particualar tractor but can provide information about how tractors work that use a ballast resistor and a start by pass system to put battery voltage to the coil ONLY while cranking for a hotter starting spark (cuz ballast is then by passed):


1) If it uses a starter solenoid like a Ford type that has an extra little I terminal, that terminal is hot ONLY when the solenoid is engaged (its other S terminal gets voltage from the push to start switch so it cranks) so when you press the start switch the feed from the I terminal effectively by passes any external series Ballast Resistor by sending that hot voltage direct to the coils input (or output side of ballast, same point electrically) BUT ONLY WHILE CRANKING.

THEREFORE ifffffff the tractor has such a solenoid and iffffffffff it has an external ballast resistor and iffffffff it uses such a start by pass system and fires ONLY while cranking but NOT otherwise, the Ballast is bad/open orrrrrrr theres another open/bad/missing wiring issue such as in the circuit from the ignition to the ballast and/or from ballast to coil i.e its such that the regular feed from switch to and through ballast and to the coil is open or broke somewhere so the only way n time the coil is hot is when the start switch is depressed......... YOU NEED A CONTINUOUS UNBROKEN WIRING CIRCUIT FROM IGNITION SWITCHES IGN OUTPUT TO AND THROUGH BALLAST (good ballast that IS NOT OPEN) TO THE COIL.

The other possibility is the Ignition switch itself is bad (or the input voltage feed isnt there) and its NOT supplying hot voltage out its IGN output (to ballast and coil) when its turned to ON. There has to be a hot BAT input feed to the ignition switch (check for that and any blown ignition system fuse),,,,,,,,,, and the IGN output terminal has to get hot when its switched to ON,,,,,,,,,and there has to be a good circuit/wire from there to and through a GOOD ballast......

2) Instead of a Ford type solenoid with an extra I terminal (it may have a regular solenoid without any extra I terminal thats hot only while cranking), some tractors used a switch contact arrangement (like a double pole switch) as a source for a hot feed to by pass any ballast ONLY WHILE CRANKING. If it uses such a switch arrangement again it feeds hot voltage to the coil (by passing any ballast) ONLY while cranking so if it fires when cranking but NOT otherwise, similarily look for a bad/open ballast,,,,,,,, or a bad/open/missing wire from the regular ignition switches IGN output to and through a ballast to the coil,,,,,,,,,,,or a bad switch that isnt supplying hot voltage out its IGN terminal when ON.......

SUMAMRY: Id be checking any Ballast to insure its continuous and NOT an open circuit,,,,,,,Id expect its resistance to be in the 1.2 to 3 ohms or so (depends on the coil),,,,,,,,,,,Id be checking the regular Ignition switch to insure theres hot battery voltage out its IGN (to ballast and coil) terminal when its ON,,,,,,,,,Id insure theres a hot feed TO THE SWITCH on its BAT inupt terminal and no blown fuses or bad wiring to the switches input (has to be voltage to the switch before it can provide output voltage),,,,,,,,,,,,,Id insure theres a good wiring n circuit from switch to and through ballast to coil........

Let us know, check that ballast and ignition switch and wiring ..........

John T

PERFECT ANSWER!!!!! JimN

Wow, thank you both for the great information. I"ll check it today or tomorrow and tell you what I found.

For my curiousity, is the only purpose of the external ballast resistor to step down the battery voltage so less voltage is applied to the coil, points and condenser to make them last longer? If I need a new ballast resistor and don"t have the exact value, should I size it so approximately 6 to 8 volts is applied to the + side of the coil?

Thanks again

A mid 50s or 60s chevy truck ballast resistor from NAPA will do fine. It is not a critical application. The cold value will be much different than the working (hot )value, so just do it. Best of luck, Jim

Thanks Jim but "Perfect" thats like NEVER say NEVER Now if you can convince my "first wife" Im ever that good lol

Take care now my friend

John T

The purpose of the ballast resistor is to drop sufficient voltage (often 12 down to 6) so the coil only draws its rated current and dont overheat and likewise the points switch whatever current they are rated to handle so they dont burn up prematurely.....

The ballast should be sized so it drops enough voltage such that the remaining voltage is what the coil is rated for. Typically that would be 12 volts down to 6 so if the coils primary is 1.5 ohms the ballast would also be around 1.5 ohms for a 50/50 voltage divider. If you have a 6 volt coil measure its primary resistance (between its lil + and - terminals) and the ballast would be near the same and typical ones are in the 1.25 to 2 ohm range

Get it????????


John T