Hey guys I have a 82' 300D and when I drive at random times the tach will drop to zero and my glow plug as well as seatbelt lights will turn on. After a few seconds it will work again and the lights will go off. Could this be a tach amp problem and are the lights interconnected to that amp somehow? Also i found a bad gp and replaced it but still get no glow light other than when the tach goes to zero while driving. Any help is greatly appreciated! Thank You

I would think it may be a grounding issue. Try installing a ground wire from the speedometer's metal housing to the large grounding point behind the cluster.

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Baton Rouge, LA
1977 300D Non-Turbo

There is a large round multi-pin connector that plugs into the left side of the instrument cluster, behind the gauges. If that is loose or damaged you will get symptoms like that as the ground connector is in there. (I just went through this after having the cluster out twice.) Also if the ground trace on the cluster is damaged.

Agree with the other respondent on running a new ground, but to ensure you cover all your bases, try running grounds from both of the tiny phillips head screws at the base of the center portion of the back of the cluster (you can join the wires to make one ground connection). This should cover you off if it's the ground trace on the cluster that's bad. If you install a quick-disconnect or spade connector in the middle it will make life easier for re/re the cluster later.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Alright so just to make sure I'm on the same page I should run a ground from one of the spedos metal screws on the housing to one of the other screws on the back of the speedo?heres a picture, Thanks for the help IMG]http://www.dieselgiant.com/mbodo10.JPG[/IMG]

Wire brush all connections on the back. A brass brush is good to use.

If your dimmer isnt working now would be a great time to fix it.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

I would suggest you make a "Y" configuration with a separate wire from each small screw going to a single quick-release connector, then the other side of the connector runs over to the big cluster of grounds that you can see when the cluster is removed.

If you would rather buy one made up, these guys will sell you one: http://www.mbelectronicupgrades.com/Cluster%20Ground%20Install%20Guide%20Rev%20A1.pdf

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22