Ok, the Keyboard, is comprised of 3 columns, the two outer columns have 5 switches each, and the center column has 4 switches. The switches are all lights. Pins 1 are white, are lamp Ground, pin 8, gray are lamp power. One side of switch is jumpered together, pins 3 & 4, and there is a black wire attached as well, which makes this switch effectively a SPDT switch. 
| KBD | TGT | |
| 1 | 2 | 3 |
| 4 | 5 | 6 |
| 7 | 8 | 9 |
| CLR | 0 | ENT |
If you look down at the switch and hold the jumper (pins 1 and 2 ) on the right side, also has the black wire. The top is the normally open side, has a yellow wire on it, so when the switch is depressed it closes. The bottom is normally closed, and has a blue wire on it.,so when the switch is depressed it opens. There are two connectors W5P1 & W5P4 coming from the switches. So there is the quandary, there are two ways to skin this cat (keyboard).
| W5P1 | W5P4 | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 15 | 14 | 13 | 12 | 13 | 12 | 11 | 10 | 9 | 8 |
| Blue | Yellow | Blue | Yellow | Gray | Yellow | Yellow | Blue | Blue | Gray |
| Cut | Overlay Power | ||||||||
A) wire each of the 14 switches to an input on a MCP23017, when a key is pressed a interrupt is generated and read the expander. Done.
B) Don't screw with the keyboard any more figure out the rows and columns a originally built. Rows go to one half of the MCP23x08 the Columns go to the other then you need a scanner, that is triggered by a keypress. Microchip has a application note AN1081
C) And lets not forget you can also achieve similar results as A) by using 2 7-bit priority that are cascaded.
