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 - Ford Part Number Trivia - by Forum Participants. "Replaced by" means the part was superseded. All of my part books date back to 1964 and New Holland have changed some part numbers. They usually put the old Ford part number on the package. I was suppressed when I looked up the part number of the auxiliary drive shaft because for some reason the part number went through a radical change and it lost its "Basic Part Number". Ford part numbers follow the following rules. Most part numbers are in three parts. The middle part is called the
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