Represent that network of wires as a directed graph.

Find the biggest tree spanned within the graph. This will be the wire that, should you ever have to replace it, will have you cancel all your other plans for some foreseeable time…

Yes, I think it was a requirement that both ends of a wire were at the same level on the pin. So you might have an additional top-level wire but you wouldn't end up with a long dependency chain.

I should also mention that the original (non-field) wire wrapping was done with an automated machine, the Gardner-Denver Automatic Wire-Wrap Machine. It had X-Y carriages with wire-wrap tools and it wire-wrapped the backplane according to a deck of punch cards. Details: http://www.bitsavers.org/pdf/gardnerDenver/SM506753_Paramete...