Hi Keith,
I wrote you direct, but here is my reply for the forum:
The kits from Elecraft were designed to work with the K3 Twin, not with a stand-alone K3 being controlled via software.
Most likely the serial cable on the radio RRC is correct - a straight through serial cable.
The supplied cable for the control side would be a null modem cable with pins 3 & 5 and 7 & 8 crossed. You would therefore have a problem if you attempted to use this cable for CAT control over the control RRC. Since you are apparently using USB for CAT, this is not the problem. Since the connectors on the null modem cable are different, you have not used this by accident on the radio RRC, which would also cause this not to work.
I didn't notice a configuration problem, but maybe I messed something. Bottom line is I would need to log onto your computer to try to figure it out, assuming it is not indeed a cabling problem (unlikely).
73,
Mitch DJ0QN / K7DX