Thank you for your answer.
Edit: glow indicator works, but spring is at the bottom, and seating it's not very viewable, but it works perfectly.
Actually, with a rather hot weather, glowing time is typically 10 seconds. But in winter, it's longer.
But glow plugs are not expensive and I'd prefer to have 2 pairs in replacement. I've tested glow plugs with z 12V battery. They became red more or less quickly.
Two questions for this kind of tractor owners: are they springs Under the seat ? Mine don't have them and it's not confortable.
Could someone post a picture of fuse box ? I don't have the cover anymore.
Thank you.