1975 originally a d-jet.
I'm studying the electrical diagram and cannot locate the small yellow wire coming from the relay board into the engine compartment. Note...not the one to the starter. I think it's for the cold start valve but I'm not sure?

It may not be a yellow wire, then. Wires can fade and change color over the years. Where on the relay board is your yellow wire? Are you sure it was originally yellow?

--DD

There is a nice yellow wire from the relay board to the double relay on a 74-75 1.8L, but not for the 2.0L.

So do you have a yellow wire that you are looking to figure out or do you not have a yellow wire and think you should have one?

I may have figured it out. It actually looks like the white wire in position 12 for the aux air valve, so I won't be using it with carbs.