I've noticed a glitch on Radeon cards under OS 9, when connected to widescreen monitors over a digital connection (ADC or DVI).
nVidia card: all is well in 9 and X.
ATi card (X): all is well
ATi card (9) using a VGA port: all good
ATi card (9) using a DVI/ADC port: black screen after drivers load, if a widescreen resolution is selected. Everything fine if a 4:3 rez is selected.
The above results were obtained on a G4 AGP with Radeon 7000 / Radeon 8500 / GF 4600. I have my original Rage 128 Pro still, but haven't used it for at least a decade.
The monitor im using doesn't have the required extra 4 pins to do that (picture 1) but in (picture 2) my G4 runs OS 9 perfectly when booted into safe-mode so, shouldn't it be an extension issue?
You're reading their advice backwards. They mean using the VGA port on your graphics card. Or plugging a VGA adapter into a DVI port on your graphics card. (This would not apply to an ADC port, as the analog pins are not present with ADC).
Then take a VGA cable from that port (or adapter) to the VGA-in port on your monitor. If your monitor doesn't have VGA-in, this won't work.
Note that a Rage 128 Pro has dual ports, but it is a single-monitor card. If you plug monitors into both ports, one will go blank anyway.
Get another video card if you can, like a PCI card. Using a monitor connected to the other card, you can test resolutions on the Rage 128 Pro.
If you are being bit by the ATi / OS9 / widescreen-over-digital issue, you can avoid it by using the control strip resolution module. It will only offer safe resolutions. The Monitors control panel offers the widescreen resolutions that cause a black screen.
Alternatively, just get a later AGP video card. The Rage 128 is a really old card, even under OS 9. Only 16 MB VRAM. Originally spec'd at 1280x1024 via the digital connection, and 1600x1200 for the VGA connection.
