> So then, I'm guessing that the 5-pin plug at J5 is where I'd hook up the
> IBM keyboard adaptor if I had one?

As Supertimer says, you don't really need this, especially if you have
an extended keyboard on the IIgs.

Anyway, in case you want to try it, I have in my hand the IBM keyboard
adaptor.

Going on the same numbering scheme as the IIc serial ports, the DIN 5 is
numbered as follows, looking into the surface of the plug:

    T

5       1
 4     2
    3

The tag (shield) is not connected.

The other end of the cable is a 5-pin molex connector, with a ribbon
cable between the two.  Looking into the face of the molex connector
(the side that goes onto the pins on the card), the pins are closer to
one edge than the other.  Holding the plug so that narrow edge is along
the top (so the locking clips for the molex pins are on the bottom), the
pins are numbered 1 to 5 from left to right.

(Let me know if you want a diagram of this in case it isn't clear enough
from my description.)

The cable doesn't go straight through.  The wiring is rearranged at the
DIN-5 end.  The end result is:

Molex          DIN-5
  1  ----------  1
  2  ----------  3
  3  ----------  5
  4  ----------  2
  5  ----------  4

> Hmm. Wish I had schematics for wiring a cable for either the RGB from J6
> or the keyboard from J5...I mean, I can do the two wires for the composite
> signal, but...the rest...

I don't have the CGA cable, but the picture of it in the manual looks
like a straight-through 10-way ribbon cable to a DE-9 female connector.
I can't tell you which wire doesn't go through (either 1 or 10).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand