Mercedes: All the gauges have stopped working, mercedes benz 300, fuse holder

Question
QUESTION: I have a 1983 Mercedes Benz 300 SD and the gauges that indicate the fuel the speed, the oil and everything stopped working all at once. In addition, the signal lights have stopped flashing. This happened two days after the glow plugs were replaced by a gentleman that services foreign cars and had to recharge the battery. Is this an indication of fuses or something else?

Please advise.

Thanks

ANSWER: Hello Patricia,
The problems you describe can be associated with a couple of things. The fact that you have had the vehicle worked on may have contributed to the failure. During the glow plug replacement a wire may have become loose and may have pulled out.
The Battery Battery should have been disconnected during the recharging operation.
You did not say why the battery was discharged but if the charger was high amperage and any of the circuits were engage, it could have cause the over voltage/amperage relay fuse to blow.

I would check all the obvious connections under the hood. Make sure the battery is in excellent condition. Diesels require considerably more cranking amperage because of the the high compression.
Check all the fuses. Corrosion causes high resistance and heating of the connections. Aluminum is very prone to corrosion. If they are the ceramic bullet type, and use aluminum burn strips, I would replace these with copper strip type. Polish the fuse holder sockets and the tips of the fuses.
Make sure all the ground strap connections between the engine and the chassis are clean and tight.

Good Luck
Robert




---------- FOLLOW-UP ----------

QUESTION: Thank you Robert,
for your quick response. The battery was totally dead and had to removed by the technician to recharge it. Should I go back to the technician to ask him to see if a "wire may be loose, or pulled out"? Or, should I check the "over voltage/amperage relay fuse" to see if blown, replace it to check and see if that solves the problem? His shop is a 45 mile drive from my home, and he is overloaded with work on so many other cars!

Please advise.

Thanks,
Patricia F. Davis

ANSWER: I would suggest that you phone the mechanic, particularly if you have a good working relationship with him/her. Explain the problem, and ask for suggestions.
I would not hurt to check the over-voltage relay fuse, and it it is blown, could be replaced very easily for less that a dollar.
When you turn the key, do you get any indicator lamps on before you start. Like: check engine, low washer fluid, bulb detection light etc.?
Good luck
Robert

---------- FOLLOW-UP ----------

QUESTION: Robert,

I would like to ask your expert advice on an issue with the fuel gauge. It seems that it gives erroneous readings when the fuel is at a certain level. It "jerks" back and forth when I have a little less than half a tank of diesel fuel. The caution light comes on and goes off several times as if, there is a problem discerning actually how much fuel is in the tank. Is there also a gauge of some kind in the tank to prompt the fuel gauge to display the amount of fuel that is actually there? Or, is there some other mechanism that is causing this erratic behavior? Please advise.

Thanks so much,
Patricia F. Davis  

Answer
Patricia,
The fuel gauge is controlled by the sending unit in the fuel tank. The unit in the tank used a float to determine the level. Many units use a coil of wire that has voltage on it. The float arm rubs against this coil and changes the wire length and thus the resistance. Through calibration the resistance it set to the dash gauge. Or there could be a loose connection between the sending unit and the dash gauge.
The gauge float can become stuck or the wiring circuit can ware out, thus the erratic behavior.

Depending on the sending unit location in the tank, it can be pretty pricey to have the unit replaced.
I would begin by running some diesel fuel system cleaner through the tank. Diesel fuel by nature is very dirty with deposits that can collect on the wall of the tanks and even the sending unit actuator. Actually bio-diesel has very good cleaning properties, as it acts as a detergent to the fuel system.
Truck stops and some auto parts houses carry bio-diesel base additives. Just remember that this cleaning action will end up in your fuel/water separator, and you should be prepared to replace the filter if you start getting any issues with the engine.

Merry Christmas
Rob