Hi. This is a normal condition in cold weather. Your truck does not use glow plugs. It uses an intake air heater and a fuel heater to help cold weather starting and warm up. When you turn the key on when its cold the wait to start light comes on. After it goes out you start the truck. A few seconds later the intake heater will come back on, it may do this a few times. The fuel heater may come on and off at random too, it likes to keep the fuel close to 70 degrees. These two heaters are a huge electrical load, and they will dim the lights, slow the blower motor, and the charging gauge will dip down. If you actually have a charging system problem your battery light will come on, possibly the check engine light. If you see the battery or engine light let me know and we'll see what's going on with that.