Yes, that is the loop.
And what you need to put to that loop is a short section of wire from the alternator to the terminal block. Just like you had originally.
The reason I said don’t use the three wire plug has nothing to do with whether it has one, two, or three wires connected to it. It has everything to do with what their orientation is. If they all match, great. If they don’t then you are just asking for trouble.
If the field wire matches the field wire and the ground wire matches the ground wire then by all means use it.
But if there’s a black with yellow wire that doesn’t go to a black with yellow wire you still have other things to worry about.
I’m not proposing you eliminate anything and replace it with a jumper. At least not yet.
Not until we determine exactly what you have, which we have not yet.
But as I just said above, if your field wire in the three wire plug goes to the field terminals of both the regulator and the alternator, you don’t need to change it.
You need to give us the rundown. Short of precise pictures of where everything goes you need to trace every one of those wires that is in the two mis-matched harnesses. Or use them as they are made and illuminate the junction block connection.
You just need to make sure that the wires go where they’re supposed to and do what they are supposed to.
In the picture that shows the new harness you said one end of the loop with the black and yellow wire is on the terminal block and the other end is on the starter relay. That’s great, but you need for the alternator to be on that circuit too.
That is done by connecting the same gauge wire from the BAT terminal of the alternator directly to the junction block.
I’m guessing it will not go through the three wire connector, but I can’t say for sure at this point.
