I have to recommend against shielded or coax for key wiring. The likelyhood that the unprotected shield "accidentally" crosses over to contact the adjacent terminal is rather high. Further, the cheap shielded audio cable tends to have some (although high) resistance shield-to-center conductor when soldered or melted which, in combination with other stray resistances (especially at higher room temperatures,) sometime keys your transmitter inadvertently (this never happened with the "old" rigs.)
Actually Vibroplex sells key cable that works well, but pretty much anything works OK if you are fine with floppy wires here and there. I have used "zip" (speaker or lamp) wire with no problems, although I have crimped contacts on the ends to prevent fraying wires.
Thanks for the heads up, I will watch out for that problem. Actually, Yaesu says they specify shielding to keep RFI from damaging the microprocessor so I better follow their lead. One of the generous members here was nice enough to send me 2 feet of good quality cable so I will be ready as I learn code.