Wilson, PS, the tractors you showed me were all gas as I recall, them neat old Cockshuts.
Were you needing to rig up some Diesels?? (I was thinking only gas tractors in my earlier post) Of course if so, there's no ignition coil backfeed problem which could keep them running due to an ignition coil backfeed like with a gas tractor (Well DUH you say lol).
On diesels I've seen many various wiring configurations (was a used tractor dealer and farmer) used to initially excite that GM 3 Wire Alternator.
I've seen momentary push switches,,,,,,,,,,,,I've seen toggle switches,,,,,,,I've seen oil pressure switches,,,,,,,,,,,I've seen relays or solenoids used, either factory ones already in place or ones that were farmer added. THERES LOTS OF WAYS TO DO IT ON A DIESEL and what's already in place (solenoids, relays, etc etc) can determine the method you choose to excite the alternator.
While you don't have to worry about backfeeding an ignition coil on a diesel and needing a resistor or diode to prevent that, depending on the wiring and system and what if any factory or farmer added relays are used for OTHER purposes, you may have a situation where a diode becomes necessary to prevent backfeeding a relay or solenoid if such is a problem on your particular diesel tractor and depending on how you wire your excitation circuit.
So Wilson, are you ONLY asking about gas tractors ??? As I posted, I've seen and used three different methods on those (Here's a repeat for your convenience):
A) Resistors (while a few to 10 or more ohms works, higher wattage units have bigger stronger easier to wire leads which is why some prefer them). The resistor method is very cheap (subject to type and quality), very easy to wire with no polarity issues, and reliable.
B) Diodes (while only a few amps suffices fine, again somewhat higher rated units have bigger stronger easier to wire leads). May cost more then a resistor (depends on size and type and quality etc), but still relatively cheap and a lot of farmers, including yours truly, have used them.
C) Idiot Lights which can serve a DUAL purpose as a charge indicator PLUS prevent run on caused by ignition coil backfeed. A lot of people liked that method for the idiot light charge indication feature PLUS it also prevented coil backfeed.
One last note, while I never experienced a resistor problem where they were used, I did see a few diodes go bad HOWEVER that may have been caused by incorrect sizing or poor quality or other reasons. If sized and installed correctly they usually cause no problems. The ones I personally installed worked fine as well as when I used a resistor. EITHER (or the idiot light) CAN WORK FINE
There ya go neighbor, this post regarding diesels and that below about gas engines should help you make your choice.
Keep in touch, will I see you this winter in Florida?????
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