Not sure why they have an extra B junction near the head tube; as you said it doesn't make sense.

I have my IA1 wired up exactly like you said you did the SC, i.e. 5 port junction A up front, B junction near the BB.

The TT and brake level wires are plenty long enough to reach the A junction you hide in the nose cone.

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the world's still turning? >>>>>>> the world's still turning