Intermittent battery drain 300CE 24V

[Ade W124]

Funny business again. After having a few battery issues a few weeks back, checked all the fuses with an ammeter and everything checked out, charged the battery up and it seemed to be holding charge fine for a few weeks then...

driving along at night a couple of weeks back and the orange bulb failure idiot light came on.. Didn't appear to be a bulb out so on a hunch I ran the wipers with a squirt of screen wash to run the headlamp wipers and the light went out. Put it down to 16 year old electrics and dicky (disabled) scorpion alarm

My wife used the car last night and as she pulled up in the driveway, the light came on again. Went to use the car tonight and found a dead battery (courtesy lights still worked but couldn't turn the engine over)

So... it would appear that there is an headlight/ tail light bulb or connection with an intermittant short...

Car has run perfectly for a month and typically it happens at moments of maximum inconvenience.

Any suggestions where to start poking about...?

Ade

 

[kid-jensen]

Adew124.

It should be possible to isolate parts of the lighting circuit by looking at the list on the fuse box and pulling out as many fuses as you can do without.

As far as I recall, the bulb warning only works when you switch on the lights, but obviously, you can switch them on during the daytime for diagnostic purpposes.

As far as tracking down faults is concerned, the fastest way to find a particular problem (assuming there's only one) is the "half-split method". This involves elliminating half the circuitry at a time and localising the fault to the other half. Then you halve it again, until the fault is tied-down (as far as possible).

If you can use this method to isolate half the lighting components at a time, it should give yoiu a fighting chance of finding the problem, even if it's intermittant.

I'd suggest studdying the wiring diagram as well, but those things are a nightmare!

 

[television]

As Paul is a good way, one thing to bear in mind is that if you are doing a leak test the ammeter should be connected in without breaking the circuit otherwise the leak path could be lost

 

[Ade W124]

thanks for the replies..

will have a look later today (got a pile of paperwork to do first )

after leaving the car (unlocked ) on charge over night was a bit disappointed to find it wouldn't even crank over this morning... will leave it charging for a bit longer and then get the ammeter out this afternoon..

Will let you know how I get on.

Ade

 

[Ade W124]

Well the battery won't take charge (over 11v) so its prime suspect... although I stupidly tried to crank the engine without disconnecting the charger - fuses are ok so hopefully not fried...

those halfords portable power packs are not up to much either, 3 seconds of cranking and then dead... suppose it will come in useful when camping.

Now trying to find a battery on a sunday

Ade

 

[television]

Once a battery has a short circuit cell it will discharge within a very short time.

For the car to discharge it over night there should be some smoke or indication of the fault

Do buy a good make and not a house brand

 

[Ade W124]

Resisted the temptation of halfords, kwik fit etc. and Varta battery purchased online.. delivered Tuesday.

Old battery was a beast to get out - its from a van or something.

Hope this sorts things..

Ade

 

[television]

You Have made a wise move there Ade, you will be ok after this

 

[42731]

I had a similar problem for months. Charge the battery and no matter what you tried to save in electricity use, the battery went down until the protection relay refused to allow starting the car. New battery cured it. If this is the problem, you will notice that the electric starter has more oomph when engaged.

 

[television]

I had a similar problem for months. Charge the battery and no matter what you tried to save in electricity use, the battery went down until the protection relay refused to allow starting the car. New battery cured it. If this is the problem, you will notice that the electric starter has more oomph when engaged.

Yes correct, the starter has a hard time with a flat battery as cranking causes it to over heat

 

[Ade W124]

New battery arrived this morning, safely installed (it fits!) car fires up - bulb failure warning light still on - rear RH tail light out, rear number plate light out, check fuse 3 - its blown. It also serves the headlamp wash wipe and instrument lights.. Replace fuse, all seems to work.

Any suggestions as to what blew the fuse, I can't find anything not working..

fuse 3: parking/tail light, warning buzzer, illumination:license plates, instrument control elements (head lamp cleaning unit)

Sneaky suspicion this is not over....

Ade

 

[Ade W124]

Sneaky suspicion this is not over....

Well it appears not.. the bulb failure light is on again.... All bulbs working (except for rhs rear fog lamp which appears to have been always been missing since I've owned the car). Fuse 3 ok, all bits related to fuse 3 appear to be working..

It says in the handbook that the bulb failure light could be related to an incorrect bulb being used - I replaced the tail light with one that looks the same from the outside from a Halfords spare bulb kit - do MBs use special German bulbs..

Quite hard to ignore the bright orange idiot light, plus the nagging feeling that something electrical is not right is starting to irritate...

Any ideas.

Ade :neutral:

 

[kth286]

The correct bulbs from Merc will probably correct it.

It is a similar situation with those small lights found inside the dash controls.

Halfords ones will get very hot. The proper Merc ones are special and will not get half so hot.

 

[Bolide]

I think the rear sidelight bulbs on the early W124s are 5 Watt and later cars are 10 Watt. Use of the wrong bulb brings up the bulb failure lamp

Another classic cause is a bad number plate light

Nick Froome
www.w124.co.uk

 

[Ade W124]

thanks guys, will have a closer look this weekend..

Ade

 

[Ade W124]

Nick, bang on the money

5w bulb, 10w holder.. halfords do a 5 and a 10 as identical looking bulbs..

now it all works again :grin:



for now....

Ade

 

[Ade W124]

Well after a 200 mile trip to the seaside and back, the orange light is back on... no bulbs out that I can see, number plate lights are ok..

Was fine for half an hour or so then came on as we hit traffic approaching London.

When I stop the engine and then restart it takes a couple of seconds to illuminate after the lights are switched on.

Will purchase a very special MB 10W tail light to see if thats the problem other than that a bit flummoxed...

Aside from that, the car was a pleasure to drive this afternoon.

Any other thoughts?

Ade :-?

 

[Ade W124]

Warning light is off again, all back as it should be

AC seems to be blowing cooler as well....

Think I might need to get the car exorcised rather than repaired.

Long may it continue

Ade

 

[television]

Think I might need to get the car exorcised rather than repaired.

Long may it continue

Ade

I think that all MBs should be