300 ignition voltage question

I have been trying to figure out why my 300 is so hard to start. It was fine till about a month ago and abruptly become very hard starting. Once it is running it does okay. I did some electrical investigation today and found a funny thing, unless it is normal and I was just not aware of it. The battery read 12.63 volts with everything turned off. When I turned the ignition on the voltage dropped to 12.29 in about 15 seconds. When I went around to the coil and checked the terminal where the hot wire comes in I had 11.62. When I went back to the battery it read 12.28. I shut the ignition off and came inside here to think about it. If the voltage is dropping below 12 with just the ignition on I assume it is dropping a lot more when I engage the starter. Is it supposed to be like that or could I have a faulty switch or some other problem? Should I open the dash and check the voltage on each side of the switch? The tractor has a 12V conversion with 3 wire alt, wired according to the Bob M wiring diagram. The coil is a new 12V coil bought a couple of months ago, at which time I removed the ballast resistor which had been in the line. The switch was a cheap one from NAPA and sometimes it will not shut off unless I pull it on and then off again. Any advice will be much appreciated.
Zach

Well all but the reading at the coil is correct but the one at the coil maybe off but it may also be correct depending on your meter. A way to see is do this. Run a hot wire from the battery in this case + side to the coil and check voltage at the coil that way. If when you do that and if you get say 12 something volts try to start it that way and see if it starts better. If it does then you have some sort of problem from the coil back to the battery in the ignition wiring. Be it a bad switch or a wire going bad which does happen or other such component in the wiring going bad. By the way that reading you got at the coil tells me the points are open. If the reading was way low as in 1-3 volts that would tell me the points where closed

You may have slightly excessive voltage drop from battery to the coil but it is not far off. This is the very exact reason that almost all manufacturers use a external ballast in ign circuit. They use that extra terminal on the starter solenoid or starter magnetic switch and run a wire that goes directly to the ign coil, bypassing the external ballast when cranking. Your normal cranking voltage at battery will be about 10.5 volts so you can see you will be getting only about 9.5 volts feeding your 12 volt coil while cranking. This lower voltage will then reduce the amperage flow through the coil and it is the amperage flowing that creates the magnetic field in coil, and when points open, field collapses and creates high voltage in secondary circuit of coil. Less magnetic field, lower secondary voltage available to fire plugs. The best way to , (if I was working on your tractor,)get a better starting machine in your case is, six volt coil , external ballast and different magnetic switch on starter that has the terminal for ignition bypass. That way you would be feeding about 9.5 volts or more to the coil during cranking. Good hot spark.

One pretty simple way to get the full voltage to the coil on start is to put a #12 wire from the starter side of the big starter switch (hot when the starter is turning) take this wire to the ballast resistor and put a 4 amp diode on the end so that the electricity can flow to the ignition, but not back to the starter. connect the other end of the diode to the coil side of the ballast resistor. That simple change is equal to the replacement of the starter switch system to add an isolation ignition bypass. If the diode is in backwards, it will melt the ballast resistor.
I am not sure I like the idea of the battery voltage dropping that much in 15 seconds. It should stay above 12.5 volts until the starter is engaged. Check cranking voltage (carefully in neutral with a helper) it should be at 10.8 or better while cranking unless it is way cold. Jim

Thanks for the advice. There is no resistor anymore since I now have a 12V coil, but I think I could do what you said about the diode anyway. It is about 25 to 30 degrees F here today. I did check the battery voltage and it seemed to be dropping into the 10.2-10.6 volt range when cranking for 2 seconds. When cranking for 5 or 6 seconds it dropped momentarily into the 9 range but then bounced back. I checked the terminals on the switch and have 12.4 on the ammeter side and 12.2 on the coil side when the switch is pulled. I do not know if that is normal or not. I put in new points, condenser, cap and rotor in the summer and I think I may replace the points and condenser again to see if that helps, and also I will get a better switch at NAPA. They had a $5 one and a $14 one and I got the cheap one at the time. Thank you very much.
Zach

I have done that also, but he does not have a ballast resistor on his tractor, rather a straight 12 volt coil. If I was testing it just for hard starting, without doing any repairs, I would just hook another 12 volt battery right to the coil and LEAVE IGNITION SWITCH OFF, to see if it started better. I would be sure to observe correct polarity in case switch got turned on by accident.

I assumed you would put the (for use with external resistor) type coil on it when using the diode idea.
If the wire from the starter switch was 12 gauge to the diode, it sure would limit the voltage drop on startup. I am not too happy with your battery voltage readings. I also assume it has at least #2 gauge battery cables. Happy New Year Jim