does sound like an earth problem , hope this helps, need to ensure no lives directly connect to earth , power goes in , out to next plug and then as above connects to earth
Check the resistor (the coil of wire) isn't shorting against it's own bracket, it should be insulated from it. Power goes into it from the LH side of that photo and out of the right to glow plugs (and warning light i presume).
Edit: Have you checked for diesel at the injectors? As mentioned above your return pipe looks rather chafed. The non starting may not be a glow plug issue
Do yourself a favour and buy the newer type glow plugs with a built in resistor in each plug. The ones you have are the original type and are a pain in the rear. They sell kits with instructions for wiring along with the relevant cables.
You may as well do it while your checking things and you wont be sorry you changed over.
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