ok match up your RGB and ground...thats done..
now you only have 2/wires left on your VGA Hack Cable.
This 2 wires just hook it to the proper H/sync or V/Sync.
First try the NEGATIVE sides and see what you get, if its not good, try the Postive side.
Now if you still don't get a nice picture, TWIST the 2/wires left from the VGA cable hack and connect this to the NEG/Vsync and see what you got.
For the WG4901 monitor that you got, it should have work when you connected the 2 wires to the NEG/VSync and NEG/HSync. Also it should have worked when you twisted the wires together and connected it to the Neg/VSync.