ATI 4870 DVI-VGA not working. Help?

Question

Howdy folks,
I was using an ATI 4870 with two DVI ports and one S-Video port on a Mac Pro 3,1 (I think) running osx 10.5 with two monitors
When we retired that computer I harvested the 4870 card to replace a GT 120  on a Mac Pro 4,1 running osx 10.8.  It has been feeding two monitors without issue, one DVI and the other DVI-HDMI.
However, I cannot seem to get it to recognize any VGA monitor or projector using any of three different connectors.  Nor can I seem to get any signal out of the S-Video port. 
My goal is to run a VGA projector with the Mac Pro 4,1, a projector with VGA, S-Video, and RCA inputs. 
As I said, I have tried three different DVI to VGA connectors.  Two of these are very similar with 29 pins on the DVI connector.  These did absolutely nothing.  The third has only 17 pins, and while it had no result with projector, when connected to a VGA monitor the computer would recognize that a second monitor was attached, but no signal seemed to be carried to that monitor.  The osx settings showed options for two monitors, but no image appeared on that second monitor.
One of the two DVI to VGA connectors I had successfully used on the previous Mac Pro 3,1 computer, but I cannot remember if it was with the 4870 or the graphics card we used before upgrading.
A Macbook using a MiniDVI to VGA connector feeds a signal to the projector without issue.
If this community can offer any help or guidance, I would be very grateful.
Best wishes-

Answer 1

The signals used for VGA are generated directly by the DVIO-I port on the graphics card, and are supplied in the bar at the right end, the four pins around it, and one pin from the top row of the grid (salmon/pink in the diagram above). A VGA adapter has no active components in it -- it just picks up those five signals and presents them on the proper VGA pins. The bar is used as the common return.
A failure is to produce a signal is not likely to be a failure in the adapter, but a failure on the graphics card.
DVI-I (Digital AND Analog) has the bar and the four pins around it present.
DVI-D (Digital only) has no bar, and the pins around it are not populated.
Diagram courtesy of Wikipedia.