You most likely need a ballast resistor in the wire from the key switch to the coil if you're running a 12 volt system. But if you install a resisitor you will need to install a starter bypass wire to the coil. This is a small wire from the starter solenoid that is activated only when the starter is cranking the engine and will supply a full 12 volts to the coil. It bypasses the ballast resistor.
One thing to remember when starting an engine, the starter comes first in the electrical circuit. It will suck all the juice it needs to crank the engine depriving the other circuits. So with out that bypass wire to the coil the coil won't get enough juice to create a good spark while cranking.
While crankning the battery voltage may drop to 8-9 volts and then if it goes thru the resistor it is cut in half so you're talking 4 volts to the coil. Not enough juice to make a spark jump the plug gap. But with the bypass wire the coil will receive the same voltage as the starter is receiving.
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Today's Featured Article - Upgrading an Oliver Super 55 Electrical System - by Dennis Hawkins. My old Oliver Super 55 has been just sitting and rusting for several years now. I really hate to see a good tractor being treated that way, but not being able to start it without a 30 minute point filing ritual every time contributed to its demise. If it would just start when I turn the key, then I would use it more often. In addition to a bad case of old age, most of the tractor's original electrical system was simply too unreliable to keep. The main focus of this page is to show how I upgr
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