About 4 months ago, I installed new Bosch GPs, a couple days ago the #2 & 3 plugs had to be replaced, today the 1 & 4, as well...tested the wires & the relay, everything fine...what gives?

Did you test the timer in the relay? Could be staying on too long.

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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

Some questions:

# What type of plugs are you using? Loop style (connected in series, with big resistance wires between each plug), or pencil style (connected in parallel)?
# Are the plugs visibly damaged? If so, how?

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'Betsy the Getaway Car' : 1978 MB 240D, 582k
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tested the relay, stays on for about 15 sec, actually, using the pencil style plugs, now that you've mentioned it, the old plugs were caked with carbon which may cause grounding, gonna ream out the glow plug holes which I think should help.