On several tractors of various brands, the starter switch is mechanical and has no terminal for a bypass to the coil. Others have a relay to the starter that has no 4th terminal for bypassing (Ford cars/trucks had the 4th terminal). If a vehicle had a ground to engage starter relay (many old Ford tractors) again no source for 12v for starting. Wiring the bypass to the battery side of any of the above, caused the ignition to be on all the time. If wired to the starter motor side of the relay or switch the bypass will work (briefly) while starting, but the ignition system will try to operate the starter motor. (the smoke rolls) The diode is a easy answer to provide 10 or so volts (cranking voltage drop) to the coil for nice hot temporary ignition "encouragement" and preventing back feeding the starter motor which has about 0.15 ohms. Jim
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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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