We've had some colder temperatures recently (-15°C) and a problem with my battery has developped. It seemed to drain excessively overnight, to the point the car would not start anymore.

So I have disconnected the positive battery terminal and put my multimeter in series between the positive terminal and the connector itself. I read 1,94 Amps. I think this is way too much... I expected something in the order of milliamps...

Next, I have kept an eye on the multimeter (still reading AMPS) and pulled every fuses, one at a time. None led to a drop in current flowing from the battery.

The fuses I have tried are in the engine compartment, and numbered 1-16, and A-H. Are there any other fuses to test to figure out where the current is flowing to?

I have had the car entirely repainted in October, all lights and door panels have been removed. I am not surprised to be getting this sort of problems... but I need some help to solve this one.

Any advice welcome!

Thanks,

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BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

I'm following this link as well:

Large Current Drain -- Please help!

I've got a few more things to look at.

Bye

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

Ben,

'Assuming no aftermarket alarm system???
" " Solar cell charger with diodes to prevent nighttime discharge?

There is a relay panel underneath the fuse box.

There are also a few relays behind (Aft) of the battery in the area with the
ECU.

1.9 amps is TOO much , no wonder the battery is low.

Please let us know the results.

I changed the voltage regulator on the alternator: No difference.

When monitoring the Amps from the alternator to the battery, I noticed it varied a lot (but I have a digital multimeter, hard to follow the figures when they start rolling!).

So I got the whole alternator rebuilt (no new ones available nearby) and that solved the problem.

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

If I follow your diagnostics correctly...
You monitored the amperage flow from the Alternator to the Battery [Here's
the assumption on my part...with the Engine not running?].
And replacing the Voltage Regulator on the Alternator did not solve the drain.
But,a "reman" Alternator did?

supposition:
Internal fault in the windings..allowing the Alternator to drain the battery to
...Where?

I am glad you found the source and remedied the problem!

Another current track lesson.

No. I was measuring charging AMPS provided by the alternator to the battery through the positive clamp of the battery terminal (with a "clamp over" type of ammeter. It seemed as it varied between 10 and 85 amps just after starting the vehicle.

Of course, there are the glow plugs also drawing current right after start up...
So this could be the explanation?

ANyways, I'll redo the drain amps from the battery with the engine turned off and see what's the current... hope it will in milliamps this time!

Bye

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

Sorry about getting things a little confusing here, but, contrary to a previous message, I just want to tell my problem IS NOT resolved.

We've had pretty cold weather recently (-20°C) and just about 1/2 hour ago, the car didn't start following some 48h left alone. The battery was totally dead, the starter motor did not even try to turn 1/8 of a turn. Just a painful little click!

I had left this issue to a local Indy just before Christmas and it now seems I will need to dig into this issue myself: I have realized I now have daylights not working at all??? Plus the dashboard has the "Failed lightbulb" reminded turned on while ALL lights are ok on the car (license plate bulbs and all corner markers triple checked and ok)...

So I'll redo my homeworks and, as usual, will post my findings.

Question: Where is the light control module located on a 1992 W124?

FWIW, I'll just remind everyone here that I had my car repainted completely in October and I have had numerous electrical gremlins since then. There was welding done on the driver door and on the driver's "A pillar".

By for now,

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

You had your present alternator rebuilt? I might disconnect the alternator heavy feed wire and insert the ampmeter in the line. Thinking maybe a leaky diode in the alternator. A rebuilder would not miss a shorted diode yet could miss a mild leaky one. They do not always totally short.
If the welding was done without proper precautions electrical wise it could have easily started a problem.
Simple stuff first make sure things like the trunk light are really out with the lid closed but a systematically removal of all the fuses should have caught that. You are basicallyleft with things that do not turn off with the key switch and as someone mentioned the security system might be suspect. With out a wiring schematic it might be difficult to isolate. Does the glove compartment light act independently from the key switch?

I have ruled out the trunk light: got a kid to go in there and closed the lid, light went out!

Glove compartment... No, I haven't found anybody to fit in there!!! So took the light bulb out and this is now ruled out as well.

Now, it seems as if the problem was worse in cold weather. I am now wondering if I would not have a problem with the heated exterior rear view mirrors. I think they only come on when the temperatures lowers below a given temperature (which I think is +5°C for my 1992 W124). This would explain why its ok in the garage but suddenly dies when sitting outside...

The driver's side is in working condition, but not the passenger side...

I now have the wiring diagram from the Haynes Manual. Not best, but certainly a good start.

To be continued!

Bye,

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

Just a couple of thoughts.

1. Don't leave your battery hooked up in those kinds of temps with this parasitic drain pulling on it. If your battery is completely drained and subsequently freezes - it's done. Sounds as if this may have already happened. If it is still capable of holding a charge, I would keep a trickle charger on it until you need it for testing.

2. Likely not your problem, but I will throw it out there now so you can check for sure. I have read of instances where a coin has fallen into the cig. lighter socket, leaving the circuit continually open and killing the battery. Best to have a quick look before tracing all the other wires.

Good luck! I hate electrical problems!!!

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

On my 1987 300TDT the typical current drain according to the shop manual is on the order of 20 mA.

I would suggest measuring the battery current drain by placing an ammeter between the positive terminal of the battery and the positive lead wire on the battery. After doing that, each of the fuses can be pulled out one by one to try to isolate the circuit that has the short.

Hope this helps.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

I agree a mirror heater or heaters is a good place to check. Although I would have thought the manufacturer would have made them operatable only with the key switch on. Otherwise every owner in a cold zone would have the issue. Still pays to check though. Seat heaters if you have them also must be on the key switch. Again to take a battery down as fast as yours does usually takes a fairly heavy drain.

I have been chasing this problem of battery drain ever since! Every time I'd leave the car for a couple days without running, it would not start.

It seems I had a current leaking through my solenoid operated backflush valve in my WVO system. This is now resolved by means of a relay that operates with the ignition ON.

The heated mirrors had nothing to do with this issue.

I must add that I also had a problem with the battery itself: the density of the electrolyte was below minimum for 3 or 4 cells (checked with a reflectometer). So even with a battery almost new (at the time of my first post here) it was not optimum.

So now, in -24°C like this morning, the car may not start, but at least it does crank a lot and I get a major cloud of unburnt diesel smoke... that's something I can live with. I have a block heater for these days.

Thanks,

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

"Question: Where is the light control module located on a 1992 W124?"

Great big sucker in the relay section of the fuse box
(AFT section behind the "Pop In" ceramic fuse portion.)

['Talk about DeLayed answer...]

EDIT:
Whoops,Your above reply #13 just "Sunk in"...
So you've "ferreted out" the power drain?
Excellent!

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'84 300SD sold
124.128