Well I'm an idiot...a moments carelessness cause hours of pain. I was doing repairs to my instrument cluster when the plastic part slipped off of the the wire that powers the clock and it touched the metal back of the instrument cluster, the part for the tachometer and the clock.

Now the tachometer does not work and the glow plug does not come on when starting the car. I also did the after glow mod from Jeremy's instructions and that light does not come on either.... the clock still works

Weird thing about the after glow...when the car is cold and I start it, the afterglow light will not turn on, but if I touch the ground wire to a ground not on the instrument cluster, it functions as normal and turns off after 30 seconds...if I touch the wire to a ground on the instrument cluster it will stay off at the beginning and then turn after 30 seconds and stay on!! Weird...

I have checked fuses in the fuse box, fuse on the gp relay, and fuse in ovp relay and they are all good...

Any ideas?? Really wish I would have disconnected the battery...

1987 300d

that sounds frustrating. i dunno about the lights, but i may be able to dig up a replacement tach.

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'77 240D, 504H, OM617.952, etc.

G'day mate,

No worries, you've probably just blown a trace in the board. Can you solder or do you know anyone who could do a small solder job?

Just above the diode marked 'V5' is a copper trace (I circuled it in red) which you've probably blown.

Just bridge it with a strand of copper similar in diameter. If you've got some cables lying around, you can pull the insulation off and take some copper from there.

Ben

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1995 E300 Diesel

Yes I would say the fault blew your ground path for the tach/clock module. The GP light also gets its ground from the metal housing of the tach/clock, unlike all the other bulbs that have 2 wire sockets.
The ground for the tach/clock has to get across to the fuel-oil-temp module, and goes out on pin 1 of the circle connector to the main ground point behind the cluster.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Are you sure you didn't just blow the clock fuse?

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I had a similiar problem with my instrument lights and window switch lights. I had burned the circuit board trace on the oil pressure/fuel/temp gauge after touching the hot lead for the clock to a metal surface. It did not blow the fuse but did burn the circuit board trace. Fortunately I had a spare gauge, replaced the gauge, all is good.

Kelly ;

Making a mistake doesn't mean you're an idiot .

Look at Ben's picture and then begin to search out open circuits , sounds like a simple enough problem although I really dislike re soldering circuit boards .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks vwnate, I know I'm not an idiot, just was about to finish when a careless mistake sent me back to square one, sure felt like an idiot!

Thanks jay_bob and Benedict! That was exactly the problem, it looked a little different than the pic. I just soldered some wire across the broken part an voila, tach and glow plug light work!

I started the project on the instrument cluster bc, after pretty much replacing my cooling system I've the past two years the gauge said the car was running hot and the needle would jump sometimes...switched out the gauges and the car was not running hot anymore!! Let that be a lesson to others in the future! When to put everything back together and pop, there goes the tach which I replaced a month ago...

But all is good! Thanks for the help!

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