That does raise the question about what is the difference in the relays and why not hook the new pin style plugs directly to the wire coming off the strip fuse? Will it do any damage to the plugs to operate them that way?
I'm not sure what you mean by 'only glow 8-10 seconds'? Doesn't the relay and timer determine the length of the glow? Do you mean, start it after 8-10 seconds because you don't need to wait any longer anymore?

By the way, stupid me. I found a second set of wiring directions in the box. The first set I read were for 4 cylinders and the second for 5 cylinders. They are VERY different with the 5 cylinders requiring the relay. So now I do know exactly how to wire it. But I still don't know why. Does anyone know why the wiring diagram is SO different for the 5 cylinder? How does adding one more plug make such a difference?

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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