Here are pictures one from the glow plug relay out of my 1984 300D. I was going over the car looking for shorts and general maintenance, most related to finding the cause of my battery drain problem.

Picture #1.
Shows the glow plug relay @ the terminal strip lugs. The phenolic plastic or whatever it is around the terminal lug is entirely cooked/melted. An interesting note is that the terminal strip fuse was not burnt or damaged visibly although as I was beginning to clean it, one end broke off.
Picture #2.
Is the glow plug relay board indicating damage to the circuits. One spot is indicated as almost burnt through.
Picture #3. Is the opposite side of relay board with more damage.

The car doe's start right up even with the internal damage to the relay.
Question #1. Can this be draining my battery by shorting out internally or staying on after it should have turned off? Attached Thumbnails

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Cliff D.
Central Illinois
1987 300SDL 200K
1984 300D Turbo 245K

You may very well have some areas of very poor performing dielectric material, but I doubt you have a dead short. A dead short with the capacity of Diesel starting battery is going to make the bad part of a circuit board change phase a couple of times. Meaning, there would be a hole somewhere where all the smoke came out when the solid copper and other stuff became plasma. So, the fact that the system still works means the resistance path for the electricity is lower through the glow plugs than the other options it has. For now.

You should be able to measure the resistance to ground from the various points in the relay. Just follow the current path and find the weak links. Or just replace the relay module as it looks like it is on its last legs. Jim

__________________
Own:
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

Owned:
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)

Thanks Jim for responding. I think just on principle I will replace it. I tried to indicate in the pictures the damaged board, which in some areas, is burnt through the board, (YES A SMALL HOLE) although visually I don't see any copper that has been turned to "plasma" In my previous post related to my tracking down this battery drain, I mentioned a cycling "clicking" sound that my ear drew me to from, in the area of the relay. Could this have been the relay, or more likely the voltage regulator? Just curious?

__________________
Cliff D.
Central Illinois
1987 300SDL 200K
1984 300D Turbo 245K

Cliff,

The battery has a lot of energy, enough to glow the plugs and still spin that high compression engine over. If there was a dead short (V=IR, remember, and the heat generated is related to I squared, so if you have near zero resistance you get all the juice the battery can muster, which is a lot, and lots more than the circuit board can handle, thus the plasma) the fuse should protect the current carrying part of the circuit and the circuit card would become a fuse for whatever parts of the circuit it feeds. The fact that it apparently still works at all is sign of its robustness and a history of abuse. I agree you should change it. Jim

__________________
Own:
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

Owned:
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)

Jim, Thanks. I don't presume to understand how it happened, but thanks for your input. I'm just looking for a miracle to get my car on the road again. The question that came to my mind in reading your explanation is, why didn't the fuse blow on the current carrying side of the board, given the damage which is there?

__________________
Cliff D.
Central Illinois
1987 300SDL 200K
1984 300D Turbo 245K

When the board gets hot like yours did, it can be a long term exposure to a lower level of current leakage or it can be a short term event with higher current. Yours appears to be the result of a longer term problem, but that is a guess. The circuit board has the logic for telling the relay what to do, so it is unlikely the circuit board damage was caused by more than about half an Ampere or so of current where normally signal level current (milli-amps) flows, with the exception of the actuating electromagnets on the relay itself, which also operate on lower current levels (lots of turns of very fine wire tells you it can not carry a lot of current). The logic end of the circuit is protected by a fuse in the fuse box, I believe, or some other 8 Ampere or so in-line type fuse.

The input and output of the high current side is protected by the fuse in the relay box. From your photos it is apparent the actuator side of the relay itself, which is in the circuit with the circuit board elements, has also suffered some damage. Eventually I would expect a spectacular failure (with plasma!) if the conditions are not corrected. Hopefully the plasma will be contained to the fuse areas. So it is a good idea to replace the damaged components now.

Jim

__________________
Own:
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

Owned:
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)