Hugh,
I cut the cable. Ran the wire through my firewall wire pass-through, along with a bundle of EGT/CHT/oil/fuel sensor wires and my mag's P-lead wire. I don't know what the big deal is about not cutting it.
I reinstalled a new connector on the cabin side with crimp D-sub pins (instead of solder like the original).
The key here is that you have to make darn well sure you connect it EXACTLY the same as it came from the factory. If memory serves, some of the wires have the same color, since there are two "bundles" within the bundle. This is from memory, so don't hate me if I'm slightly off here...
But my point is that I cut the stupid thing because the last thing I was gonna do is poke a giant hole in my firewall just to run a wire that could be reconnected on the other side. 900 hours and not a single issue related to this wiring (I did have an issue with my own coil wiring, but that's another story that I think I've already told you about).
Another option that does not require cutting & reconnecting the wire involves running it through one of the little "notches" along the upper outside of the firewall, where the firewall flange is interrupted along the curve. Essentially enlarge one of the notches, slice a snap bushing, and there you go.