electrical issues - Mercedes Forum - Mercedes Benz Enthusiast Forums


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Old 12-22-2016, 05:00 PM
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Default electrical issues

hi i am having a strange problem with my s class, the electrical power seems to fluctuate, the steering wheel lights flash and the other interior lights do the same.

many thanks james
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Old 12-26-2016, 08:47 PM
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Hello, If I were you, I would look at my battery connections first, Both need to be clean,lightly greased, and tight. Next with the car shut off for an hour or more measure my batteries resting voltage. 13.5 volts is ideal. If not charge it with a charger. Then walk away for an hour. If the voltage stays fine, leave your meter connected, and start the car. Turn on the lights and heater as well heated seats if you have them. Voltage should drop on start up, then in a minute or two, rise to about 14.5 volts as the battery recharges, then drop a bit and stabilise around 13 1/2. If your alternator has a sticky or worn too short brush this is where it will show up. On a warm day with almost no load, a 1/2 working alternator can recharge a battery . With a full load it still barely may be able to. However may well give you your symptoms.
Just a note , a battery with one failing or failed cell needs testing and replacement. It is sometimes hard to tell if its your battery or alternator, and can be both. Good luck Allan
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Old 01-02-2017, 04:00 PM
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hi going into a indy in glasgow on Wednesday morning, fitted new battery it seems as it loses the memory? runs great for a little while then no fuel gauge and power.
the strange thing is when you use anything electrical it seems to stutter needing you to push the button a few times before the operation is done, i.e the windows go down in stages and up the same, the seats do the same.

any ideas of why the power shorting this includes the interior lights on ashtray, steering wheel ?

confused but getting there.
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Old 01-02-2017, 04:46 PM
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Default electrical issues

Hello, Glasgow. Wow a long distance from me. Further let me explain why I advised checking basic battery and alternator functions first. Your alternator has 2, brushes and at least 2 diodes <one way electrical gates>
Most electrical components in modern automobiles run best inside a rather narrow voltage range. An example of this is headlights still work <although poorly> at 6 volts, vs fuel pumps that usually stop at about 10 volts. Things like your relays have a tiny internal spring and if its coil voltage drops below about 11 volts things start to flicker and shut down.
Where I live in Canada, smart owners know that due to harsh cold starts and heavy electrical loads due to that cold, means they will require a new battery fairly often. I maintain 8 vehicles , and average 5 winters per quality battery. Alternators here can fail prematurely due to the same reason, as well a stuck or worn out brush, or failed diode..
It takes a mechanic a short time
s to properly analyse your charging system. Often a failing battery or corrosion of battery terminals kills an alternator. Hope they find something simple . Happy New Year Allan
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Old 01-03-2017, 07:23 AM
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thanks allan,

yes the scottish climate eats cars and battery's to. The car stood for a year before i goot it as the person was ill. there are signs of water in the rear seat/sam earlier and what looks like a sam from a 0/3 year car installed.
\my thoughts are that the sam has not been coded for the car after being replaced from what i can find through the forums.
I have an indy who worked for merc for many years looking at it tomorrow on his older star machine.
thanks for the help so far and happy new year to you all...

I posted a youtube video of the problems if you search mercedes electric fault\

thanks james
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Old 01-08-2017, 01:01 PM
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ok after some serious help from the forum and reading many posts i decided that the drivers side module was the cause of the fault, as the side lights were not working.

So i went to a breakers and got the drivers side sam and a new over head console as the star machine said it was faulty.

replaced the drivers sam and the ohc and light issue fixed!!!! but no auto lights..
i then replaced the old ohc unit and hey presto auto lights and all lights working...

whilst i was messing around with the console my brother was messing around with the ashtray and i noticed the srs light was flickering and the air bag light on the shifter light for the first time.

so i think i will strip the centre console and check the connections and the earth.

no only a abs ring and the M55 flaps to be done and were nearly there.

thanks for the help so far,,
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Old 01-26-2017, 02:34 PM
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so far so good, new abs sensor and all the warnings disappear!!
only srs light on due to passenger seat mat malfunction..

on pre facelift cars I was lead to believe it could be switched of in STAR or by changing some wires?

any help would be great.

thanks james
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