When I put the pencil style plugs in the 77 300d, I just disconnected the ground, hooked the first one to the same wire the first series plug was connected to and put jumper wires between the plugs. Been working fine this way for years.

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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