Just one Bulb in Backlight!!! Hilfe

hi can anyone help with the installation of the backlight. I have a MZ-ETZ 251. The Backlight I have currently have 2 bulbs. This light is broken and I've bought a new one. The surprise is that when I open the new Backlight Just have 1 bulb.
My question is if I connect the positive of 21 w (brake) and 5 W (Backlight) together, may have a breakdown?? Work well the backlight and brake light in this way???
My question is if I connect the positive of 21 w (brake) and 5 W (Backlight) together, may have a breakdown?? Work well the backlight and brake light in this way???