Delco 12SI draws 2-3 amps on the excite-field circuit. I've never blown a pair of 3 amp diodes in parallel yet and I've got 8 tractors wired that way (with Delcos or Hitachis).
Biggest problem I've had when using resistors instead of diodes is run-on with diesels. Many diesels with 12 volt electric shut-offs will keep going even with only 3 volts. Diode at less then $2 is kind of a no-brainer. Works with gas and diesels and always allows shut-off.
Another way to wire a Delco SI series with no resistor or diode is with a generic automotive type ignition switch. The kind that has separate ACC and IGN terminals. Wire the ignition to the IGN term, and the alternator excite wire to the ACC term, and you're all set. The two are isolated when you turn the key off.
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Today's Featured Article - Tractor Profile: Allis-Chalmers Model G - by Staff. The first Allis-Chalmers Model G was produced in 1948 in Gasden, Alabama, and was designed for vegetable gardeners, small farms and landscape businesses. It is a small compact tractor that came with a complete line of implements especially tailored for its unique design. It featured a rear-mounted Continental N62 four-cylinder engine with a 2-3/8 x 3-1/2 inch bore and stroke. The rear-mounted engine provided traction for the rear wheels while at the same time gave the tractor operator a gre
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