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Old 03-05-2003, 09:17 PM
JimSmith JimSmith is offline
Join Date: Jul 2001
Location: Woolwich, Maine
Posts: 3,598

After reading your response, I went to consult my manuals. You may be correct in the belief that there is no fuse in the power supply from the battery to the glow plugs, and the relay operating circuit.

I only have detailed schematics for older 220D types, and they had that actual glow plug on the dash above the steering wheel, which did not involve a relay. But power from the battery gets to the light switch and from there to the key operated start/run system, without passing through a fuse of any kind.

I have a crude schematic for the early W123 models from a manual for the 1974-76 240D with a supplemental section on the W123. This schematic shows the power to the glow plugs themselves coming from the plus side of the battery and going through the light switch (terminal 30) to the glow plug relay, while the power to activate the relay comes from the light switch (also terminal 30) and goes to the key operated starter/preglow switch. This implies there is no fuse in the supply line to the light switch on these models as well. I am having a hard time believing MB would provide a hot wire to the interior of the car without a fuse but it appears they have been doing it for a while.

If you have a later model some of the details of the relay change, but I am fairly certain the power for the plugs and the control of the relay runs the same route. If you need it I can scan and post the schematic.

There is a fuse (50 A) for the glow plugs themselves, and it is mounted on the firewall on the early W123s (on the front left - driver's - side inner fender on later ones).

Sorry if my first discussion was bum dope. Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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