The220D,

A 1970 220D should have the old series style glow plugs, with the extra one on the dash behind the "salt shaker" screen. That one on the dash should glow while the normal ones in the engine are doing their job. Also the heavy wires with the hairpin bends that run between the GP's should be getting hot during glow time. If these things are not happening, and you have this style glow plug, they are not working. Also with this style GP, the loss of one will take out the whole system like the old Christmas tree lights.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150