In my case it was the wire on the last glow plug (the on nearest the radiator). I just replaced the wire with 10 AWG wire to the block. In my case the plugs wouldn't get hot enough until it was replaced. Your picture is extraordinarily blurry and it's hard to tell although the wire you say is corroded seems to be the same as mine.

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'84 190d 2.2 - Silver
Converted to 5-Speed
'84 190d 2.2 - Blue
Factory 5-Speed

'76 300D (W115)
Sold, found again in less auspicious circumstances