A US 115 body 240D would have the old push/pull type starter/glow switch.
In this system there is no glow until you are pulling and holding tention against the spring loaded glow switch. just placing the knob in a position doesn't do it. The act of glowing uses so much current that the electric bulbs in the dash will dim when the system is working.
If it is working after 20 seconds or so the heater element behind the grill (black circle with holes in it) will start glowing red. It glows because it is HOT. I used to start my old 190Db by holding it till my finger felt the heat and then pulled to start.
During starting the dash heater coil is disconnected (by-passed) to increase current at the lower voltage of cranking. The engines glow plugs will continue to glow till the starter is released.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 04-21-2000).]