The current must go in to the plug, thru the loop, out the plug and over to the next plug without this loop being shorted. So there are two points of connection on the end of each glow plug. One is small and one is large I think. The heavy loop wires attach at these large and small connections and are separated from each other by the insulator. The hot wire goes to the small connector at the plug nearest to the firewall and the ground wire goes to the block from the plug nearest the radiator.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13