The first thing you need to keep in mind is that the G7400 outputs a PAL signal. Regardless of whether you use SCART, RGB or modify your G7400 for composite video, you'll need a monitor or TV capable of displaying PAL. Although some newer TVs have PAL capability, the standard in America is still NTSC. If your monitor is NTSC-only, but has a vertical hold, you may be able to play your G7400, but the picture will probably show little or no color.

Video Options

SCART

If your TV or monitor has an SCART input, you're in luck! Just be sure to buy a G7400 that has an SCART port (see Step 1 for further information), and connect it to your TV that way. You will need an 8-pin DIN to SCART cable. Such a cable was originally packed in with SCART model consoles, but that's no guarantee it'll still be included with yours. Unfortunately, I'm not sure where you can purchase replacement cables.

RGB

The simplest way to use RGB video is if your G7400 has an SCART port (see Step 1 for further information). You will need an 8-pin DIN to RGB cable. Be careful when shopping for one; 8-pin DIN cables are scarce. DIN cables with 6 pins are easy to find, but they won't work. You may have to build your own 8-pin cable; refer to these pinouts for help. Once you have a suitable cable, simply plug one end of the cable into your G7400 and the other into your monitor, and you should be good to go!

If your G7400 has an SCART port and you have the 8-pin DIN to SCART cable that came with it, you may be able to purchase an SCART to RGB adapter cable rather than building your own. Retro Gaming Cables, a manufacturer based in the UK, offers a number of SCART adapter cables. Depending on your TV or monitor, they may have an adapter that will work for you – and they ship worldwide! Of particular note is their Commodore 1084S-D adapter, which allows SCART to be displayed on a Commodore 1084 monitor.
Click here to shop at Retro Gaming Cables.

If your G7400 does not have an SCART port, you can still get RGB video from it if you're willing to do some work. You will need to perform the RGB Modification. This modification requires an analog RGB monitor to work.

Your monitor must have RGB inputs and be able to display PAL. A reasonably low-cost RGB monitor is the Commodore 1084, a favorite of classic gamers everywhere. It should be compatible with the G7400.
Click here to search for "Commodore 1084" on eBay.

Composite

If you've performed the Composite Modification, then all you need to do is plug it in. Remember: your TV will need to be capable of displaying PAL. If you connect your G7400 to an NTSC monitor, and it has a vertical hold, you may be able to see the picture, but it will be in black and white. In any case, composite video will result in a less clear picture than RGB or SCART. Use it as a last resort.

If you are unable to obtain a PAL monitor, you can purchase a composite-to-NTSC video converter. Beware, though. These devices tend to be expensive (about $200). Cheaper models are available but usually result in a terrible picture, if they work at all. One converter that has reported to work well with composite-modified G7400 machines is the Atlona CDM-660.
Click here to purchase an Atlona CDM-660 on Amazon.com.