190e 1986 electrical problem question
 

The other day I did something really stupid and grounded out a jumper on a coolant snsor to keep the electric fan on (its 108 degress here in the desert)...one of the alligator clips grounded out on the engine. There was a puff of smke a puff in the dash and the the car cut out, will only run 5 seconds before the engine then dies, yet it will start and run every time for the 5 seconds.
My theory is that I melted a wire that has fooled the engine to think that the engines not running and the computer shuts down the fuel pump. All the fuses are intact and everything works fine for the 5 seconds its running except I noticed the tachometer does not work now. Any advice or where to start troubleshooting this would be appreciated. :o
Thx John

Hi,

Things could actually be worse!! You believe you saw smoke from somewhere and if so then that gives you an idea where to look. Also you have a clue in the broken tach. Also if there was smoke then there should be visible evidence of something "burning up" that you should be able to find through visual inspection. Obviously a schematic and the ability to read it (I am an electronics guy but still struggle with the Mercedes schematics) will help but it is not absolutely necessary. Some smart person might tell you where to look. In the mean time if you are so inclined, pull out the area where the smoke was and inspect for the burned area. Then fix what you find. Good luck!

Thanks for the insight I'll pull the dash pod and check for the burnt wires on my next 3 days off. Your logic makes sense, is it difficult to replace a tach if I need one ?

I have no idea! However, I am guessing that the tach is not bad. I am guessing that something on a circuit board burned up. However my crystal ball is getting cloudy.... A schematic might help you if you can find one. You might try your local library. Mine does have car schematics.