I built a dual-monitor cable for my Rainbow three years ago for
	about $20 using parts from Radio Shack.  Rather than build a
	cable long enough to reach from my system unit to both of my
	monitors, I built a short "Y" cable that I connect to the
	standard cables that came with the monitors.

	The Rainbow 100 graphics option generates four signals - Red,
	Green, Blue, and Monochrome.  The standard color monitor cable
	actually takes the monochrome output and feeds that to the green
	input on the monitor. (The green signal goes nowhere.)  The
	Rainbow with graphics option may, under program control, send
	either the monochrome signal from the graphics board or the
	output from the motherboard character generator out on the
	monochrome pin.

	Most commercial sofware actually sends the "green" signal only on
	the Monochrome output, with no signal sent on the Green output.
	Thus, if you wire the cable so the green signal goes to the green
	input on the color monitor, you will not see the green portion of
	your graphics.  (The high four bits of the color map in GWBASIC
	controls the true GREEN signal - this isn't documented.)

	A dual monitor system is capable of displaying text on the
	monochrome monitor simultaneously with graphics on the color
	monitor.  If you wire the cable so the monochrome signal goes to
	the green input on the color monitor, all text from the
	motherboard will be displayed in green on the color monitor.  You
	will lose one of the advantages of having dual monitors.  

	To get around the problem of sometimes needing the monochrome
	signal and sometimes the green signal on the green input of the
	color monitor, I built a single-pole, double-throw switch into
	the plug that goes into the back of the Rainbow.  I was able to
	mount a switch designed for PC mounting onto the connector cover.

	Note that the +12V and Grounds carry the power for the keyboard
	and monochrome monitor, so be sure the cable you use is adequate
	- I used two wires from the cable for each +12V and Ground, and
	soldered them together at both ends of the cable.

Dual Monitor Y-Cable Construction
"nc" = Not Connected

+------------+------------+                            +--------------+
|   Signal   |15pin Female|                            |  15pin Male  |
|    Name    | MBd. Conn. |                            |  Mono Conn.  |
+------------+------------+                            +--------------+
                  pin                                         pin
                .____.                                      .____.
  Red Shield    |  1 |>-------+                             |  1 | nc
                |    |        |                             |  2 | nc
  Green Shield  |  2 |>-------+                             |  3 | nc
                |    |        +---------------------------->|  4 | shield
  Blue Shield   |  3 |>-------+ +----------------------+--->|  5 | Ground
                |    |        | | +--------------------+--->|  6 | Ground
  Mono Shield   |  4 |>-------+ | | +-------------------+-->|  7 | +12V
                |    |        | | | | +-----------------+-->|  8 | +12V
  Ground        |  5 |>-------|-+-+ | |                     |  9 | nc
                |    |        | | | | |                     | 10 | nc
  Ground        |  6 |>-------|-+-+ | |                     | 11 | nc
                |    |        | | | | |       +------------>| 12 | Video
  +12 V         |  7 |--------|-|-|-+-+       |             | 13 | nc
                |    |        | | | | |       |   +-------->| 14 | Kbd Recv
  +12 V         |  8 |>-------|-|-|-+-+       |   | +------>| 15 | Kbd Xmit
                |    |        | | | | |       |   | |       |____|
  Blue          |  9 |>-------|-|-|-|-|-+     |   | |
                |    |        | | | | | |     |   | |
  Green         | 10 |>--+    | | | | | |     |   | |
                |    |   |    | | | | | |     |   | |
  Red           | 11 |>--|----|-|-|-|-|-|---+ |   | |
                |    |   | sw | | | | | |   | |   | |
  Mono Video    | 12 |>-- \---|-|-|-|-|-|---|-+   | |
                |    |        | | | | | |   | |   | |
  (Not used)    | 13 |        | | | | | |   | |   | |
                |    |        | | | | | |   | |   | |    +--------------+
  Kybd. Recv.   | 14 |>-------|-------------------+ |    |  15pin Male  |
                |    |        | | | | | |   | |   | |    |  Color Conn. |
  Kybd. Xmit    | 15 |>-------|---------------------+    +--------------+
                |____|        | | | | | |   | |   | |        pin
                              | | | | | |   | |   | |       .____.
                              | | | | | |   | |   | |   +-->|  1 | Red shield
                              | | | | | |   | |   | |   +-->|  2 | Green shield
                              | | | | | |   | |   | |   +-->|  3 | Blue shield
                              +-|-|-|-|-|---|-|---|-|---+-->|  4 | mono shield
                                +-|-|-|-|---|-|---|-|--+--->|  5 | Ground
                                  +-|-|-|---|-|---|-|--+--->|  6 | Ground
                                    +-|-|---|-|---|-|---+-->|  7 | +12V
                                      +-|---|-|---|-|---+-->|  8 | +12V
                                        +---|-|---|-|------>|  9 | Blue
                                            | |   | |       | 10 | nc
sw = single pole,                           +-|---|-|------>| 11 | Red
     double throw switch                      +---|-|------>| 12 | Green
                                                  | |       | 13 | nc
                                                  +-|------>| 14 | Kbd Recv
                                                    +------>| 15 | Kbd Xmit
                                                            |____|
Note:  The color monitor cable that comes with the Rainbow
Graphics option has the Green signal on pin 12, instead of pin 10.