I have a '95.
On my '95 there is a wiring connector in the center console near the gear selector. I remember it has a yellow wire. I think it might be a yellow/brown pair.
That, for my car, is the security switch interface that allows the reprogramming of the security module to accept key fobs. There's a lengthy procedure for matching them up that requires a switch (or two bare wires) connected there. The procedure is identical for an XJ6 once you locate these wires.
I've been moving servers around and the document I need is hiding in an archive file. But searching forums should locate this procedure pretty easily.