hola yo tengo el mismo problema consegui algo pero no estoy seguro si funciona te mando este link y si tienes la solucion te agresco si la compartes
http://www.networktechinc.com/technote.html http://pinouts.ru/data/MacVideoToVGA_pinout.shtml
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Use this adapter to connect a standard VGA (or higher) monitor to your Apple Macintosh.
15 pin HIGHDENSITY D-SUB FEMALE connector to the monitor cable Scheme supports multiple resolutions up to 1024x768 (1152x870), and supports multi-sync monitors like a Viewsonic or Hitachi.
* Connection as shown wil allow multiple resolutions up to 1152x870. Reverse diode to limit resolutions to 1024x768. The Mac Centris, Quadra, and later systems frame buffer determines what type of display is attached to the video connector by examining the state of 3 sense line pins.
The Mac Quadras, Centris series, and later models should support any display, whether from Apple or from another vendor, that meets one of the following specifications: