I upgraded my 220D to automatically controlled 'pencil' glow plugs. The starter function on my pull-to-start knob quit, so I wired the starter solenoid up to the 'glow' function on the pull-to-start knob, and the glow plug controller to a key-controlled circuit. Works great! Getting the pencil plug controller might be cheaper than a new 'pull to start' knob, and it'll help you get going in the cold (I've started up the 220D in temperatures as low as minus 2 with the pencil plugs).