If you have one it should be on top of the receiver drier. I have a 300D and mine had a little black paper tab that was never removed so I just peeled it back and there it was! It would help to know what model you have! Not all models will have a sight glass. that was on most older models because that was how you knew when you had added enough R12 to your system. Newer models that use R134 don't need the sight glass. Is your 126 the vehicle in question?