More info in addition to ray_mcavoy's great info. I was just about done typing this when he posted, so I thought I would go ahead and add mine:
Discussion here in this post, about 12SI and CS130 alternators and the wiring for them. Post #17 by VetteVet has the diagrams and pictures and lots of great info. He's suggesting an 85 ohm 5 watt resistor.
http://67-72chevytrucks.com/vboard/s...35#post8254935
Here is a guide from AAW:
https://www.americanautowire.com/PDF...20IN%203.0.pdf
They mention you can use anything between 35 ohms (5-Watt resistor) and 500 ohms (0.5 Watt resistor). The larger number of ohms the less current it will draw so that means smaller watt rating would be fine for larger number of ohms. I wrote an email to AAW to ask them what size resistor they put in the AAW ready-made adapter they sell, and Marc DeMontigney wrote back and said 510 ohms. Forum member driller35 wrote in
post #80 of the "Alternator question" thread I mentioned above that the ACDelco adapter has 511 ohms in the wire, so I'm thinking that is a 510 ohm resistor plus small amount of wire and connector resistance. Resistors have a certain amount of guaranteed tolerance, and that is what percentage different number of ohms that they actually are compared to what they are marked or sold as. So 500 ohm resistor is not going to be exactly 500 ohms, but it will be close enough for Chevy work.