Actually, this isn't a complex issue at all. (No disrespect to Ron).
The issue is wiring a SI
alternator, so the regulator is straight-forward and takes queues from it's predecessor, the DN line utilizing external regulation. The queues being actually providing a path from switched power directly into the rotor windings.
As I stated in my earlier post, with the SI configuration, the #1 (aka dummy light aka excitation terminal) actually provides current for not only the activation of the electronics in the regulator but also becomes to the initial source of current for the field (rotor).
One side (one slip ring) of the rotor is directly connected to the #1 terminal. Electrical current has a path into the regulator as well as the rotor. If the regulator is turned on by sufficient voltage to bias the circuitry "ON", then the other side of the rotor now sees a ground through the collector of the main switching transistor in the regulator. Thus a few amps
will be drawn thru the #1 terminal as the rotor now has a complete current path of B+ to ground.
This is why the Delco Remy document posted by Ron a long time ago indicates to use a 5 amp rated diode if there is no other means of current limiting in place. The rotors in the SI models can easily draw roughly 4 amps at over 12 volts.
Don't confuse the SI with the CS regulator system. The CS is light-years beyond both the DN and later SI systems.
Again, as I stated earlier, with the CS configuration, the excitation line is only used to activate the regulator as well as provide feed back (by pulling the line low for an indicator or pull-up resistor in a body control module in modern vehicles) for a non-charging state. Because you are "signaling" a microprocessor, you can use high value resistors such as 470, 510 ohms etc. The CS regulation system sources the larger current for the field from the B+ connection (direct battery voltage) at the alternator, it doesn't draw significant current of any kind thru the "L" or "I" terminal.
Once the "excitation" line is turned "on" for the CS, then Pulse Width Modulation is incorporated to provide control for the rotor. The "load carrier" having to deal with the current through the field is shown as "TR1" transistor.
There's no debating the functionality of the 3 different types of systems we discuss--the DN, the SI and the CS.
What is up for debate is the best way to provide the turn-on for the regulators.
Since this discussion is/was? about the SI series, as I stated the original poster's plans are fine. The diode will absolutely prevent any run-on condition even if his excitation line is tied directly to the IGN1 terminal of the key switch--which is directly linked the ignition system. The resistor will aid in limiting current.
Limiting current is good, as long as you don't limit so much that you risk not providing enough to initiate excitation when the vehicle is first started (which of course is to ENSURE charging unlike my least favorite alternators--the 1-wire alternators).
Why limit current at all?
Using a diode is quick and simple, but it provides no current limiting other then it's inheirant forward voltage drop. Do you honestly want a battery drain of a few amps when using the ACC position of the key switch if you tie into the accessory circuit like GM did on pre-1972 Chevelles? Do you honestly want a battery drain of a few amps when the key is on and the engine stalls out OR you/your mechanic has the key "on" with no engine running while performing testing/troubleshooting? Do you honestly want this drain present during engine cranking (if you tie into IGN1 circuitry) when all extraneous loads should really be shed to aid in starting? These examples are why it is good to provide resistance for current limiting.
Resistance wire was used in the original GM designs employing the DN and SI systems. The length of this wire provided the power rating as the length helped dissipate heat. When we are talking about SI's in particular (which used a more current hungry rotor then the DN's), you soon find out why you need appropriate wattage resistor ratings.
Anyone who doubts me, you can do a simple experiment. Put an ammeter in-line directly from a non current limited battery connection (like the main lug rear of the alternator) and read what the current is when you connect into the #1 terminal.
(Leave the #2 sense line still connected to battery voltage, but have the original #1 wire from the harness disconnected).
Or we can have Tom Mobley
Turn your key "ON" without starting the engine. Grasp the 2 watt resistor in your bare hand and leave the key on for a minute. On second thought, you probably don't want to do that
As far as using 1 amp diodes in the excitation circuit, it is entirely possible, based on what current limiting means are already in place.
There's no "givens" for anyone unless we know the whole picture of how you are setting up the circuit. This is especially true when gearheads install CS alternators in old cars as it can get tricky to properly
set things based on how GM wired these cars--with resistance wire from the ACC circuitry alone, some with resistance wire from the ACC circuitry with a dummy light paralleled, but tied into the IGN circuitry (for dummy light cars) and later resistance wire tied into the IGN3 circuit which is "ON" when the key is "ON", not in accessory, but is shed during cranking.