I have a question about the dichro head on the Beseler.

It has two cords, a grey one and a black one. The instructions say that one of them gets plugged into the wall and another gets plugged into the timer. Does this mean that the bulb stays on all the time, and the timer just opens a shutter or something? Because it gets very very hot in my darkroom as it is. There's no way I would be able to use an enlarger that was on constantly.