Tonight I continued the saga of fixing up my '78 300D. The repair of the odometer was to be the last thing before I started using the car as a daily driver.

So, I had the instrument panel out and fixed the odometer with only a minimal amount of swearing. When I put the panel back into the dash, I got everything hooked up and turned the key but saw no glow plug light. Took the panel out and checked the connection as well as the bulb. Stuck the panel back in and still no joy.

Not only did I lose the glow plug indicator light, I lost the glow plugs themselves! After this weekend's tuneup which included a ton of work, the car was working perfectly! Quick startups, good power, everything working just right. After a drive this afternoon I took the panel out to fix the odometer and now this. No glow plug function and the car has to be working reliably by tuesday.

So, any suggestions? Could I have missed a ground wire somewhere or could my glow plug relay be fried? Is this just a coincidence or did I screw up the car in some way?

Thanks all.
Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

Sounds like a blown fuse. Or a bad connection. When ever you play with something with lots of wires attached some thing extra will go wrong. Many of us would not bother fixing an odometer if it was the only thing wrong with the instruments. Too big chance of some thing else going wrong as you have discovered. Check all fuses & the main plug to the instruments.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Main instrument plug is good, as far as i can tell. Everything works except the glow plugs which is frustrating. Anoter frustrating thing is that I found the glow plug fuse box. Or at least, I think it *was* the fuse box. Located right behind the valve cover on the firewall just a bit to the driver's side. It looks like the screws and fuse were dug out of the block one day long ago. The glow plug power supply wire had been spliced apparently in the place where the fuse block was but I thought the wire had just been yanked on or burned or pinched or accidentally cut so I didn't think anything of th esplice until just a little while ago.

So now that I have the relay directly linked to the plugs with no fuse protection, do I check the relay for proper function or can I assume that it's toast?

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

X2 on checking the fuses and especially the 80amp in the GP relay. Pull the cover, and you will see the strip fuse.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I can't even find the GP relay. There are 4 nearly identical relays under my dash and following the wiring harness is no help. Like I said in my earlier post, I think I found the remains of my glow plug fuse block if, in fact, the relay doesn't contain a fuse itself.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

OH 78 300D, DUHH...... All of mine have the relay on the left inner fender.

Your relay is under the dash, and a silver can, but on the firewall is where the fuse is? think it is a small black box. from my recollection in the PNP yards.

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Yes, the fuse box for the glow plugs I believe is located right behind the engine, close to the #5 glow plug. I say I believe because there is the remnant of some plastic box there that has had some awful surgery done to it. I just found a fuse box replacement for super cheap but that doesn't help me with the relay itself.

Sitting in the driver's seat, there are a few aluminum relays that I can see with the instrument panel out or with the lower dash kick panel down. One is mounted to the bracket that the parking brake is on. One is farther back in the dash, higher up and close to the firewall. One is close to the steering column and one is a little further back and down (about halfway between the firewall and the dash.) These all look quite similar and I'm not sure which one could be bad.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

All of those aluminium relays do other stuff.

Why not click on buy parts at the top of this page and look for a picture of what you want? And if there's no picture there there's always google images. It might be easier to find it if you know what it looks like and if someone has moved it from where it should be.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

"Glow plug relay" is not found under buy parts. At least, not for my year. There are only a few images of what the relay looks like that I can find. Out of the car. I know what it looks like, I don't know which one is the glow plug relay. I don't even know if the glow plug relay is at fault, really. That why I'm asking advice here, in case someone knows how I can suss this problem out or if I'm looking in the wrong place.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

First thing: If the relay is bad, you can make the car function by hot wiring the plugs for 30 seconds at the first plug or at the location of the former fuse box on the firewall. Use some heavy gauge wire and jump from the positive post on the battery to the first plug. Remove the jumper wire once the car starts.
Secondly, you should have series plugs with the heavy squiggly wires between them. It is far more likely that one of the plugs has failed than that the relay has failed. Once one of the series plugs fails, none of them will work. You can check whether it is the relay or the plugs by seeing if you are getting 12 volts at plug #1 (or #5) nearest the firewall with the key in the glow position.
Thirdly, if a plug is bad, use the opportunity to swap in the retrofit pencil plugs as your car will start more smartly with them than with series loop plugs.
Lastly, if one of your loop plugs is bad, you can make the system function with 4 plugs by putting a jumper wire from the input to the output wire on that bad plug as a temporary fix. One way to accomplish this 'jump' is to remove the porcelain insulator that separate the input and output wires and allow the two wires to touch each other.

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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

Have a look in the pictures in this thread

http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/277309-handful-om617-glow-plug-relays.html

it will be something similar looking

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

But don't bother investigating the relay until you determine whether or not you have 12 volts for 40 seconds or so at the fuse junction on the firewall with the key in the glow position.

__________________
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

nope.
it's not one of those relays.
your relay is under the dash, I'm pretty sure it's the one bolted to the steering column. it is silver. and it'll be the one with a small harness and a large single black wire leaving it.
you say the fuse block is hacked? can you take a picture of it for us to look at?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I'm sorry to have thrown in a such a terrible Red Herring! Listen to John Phil_F_NM (and Kerry!)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Here is a photo of the engine compartment. What I think is the melted and carved up fuse block is circled in red.



I'm going to take down the cover panels under the instrument cluster again and see if i can find the offending relay. The only issue is that I've read about three possible locations for them, two of the locations under the dash.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson