w124; battery drain;Is there a secondary fuse box?
 

1995 E320 wagon; battery drains over night. (If battery is disconnected overnight, battery is strong next morning.) I disconnected the negative battery terminal, and put a test light in series. Light is bright, indicating significant current flow. I pulled every fuse in the engine room fuse box, just ahead of driver. The test light never went out! Is there another fuse box?

The car has no aftermarket gizmos hot wired in.

Side note:
The ASR light come on with the second start-up of the day, but does not seem to have any effect.
When the battery cable is connected/disconnected/ connected, there is a click click click sound from what I assume is the ABS pump, in the front/driver's side of the engine room (many steel pipes going into this unit). If I pull the two relays out of this unit, the click stops of course, but the test light still glows brightly, indicating current.


The test light I refer to is between the batt neg terminal and the disconnected neg batt cable.
Thanks for your thoughts.

You're on the right "Track"
 

Notorious W124 "Phantom Drainers"

1.Antenna
2.Trunk Light switch AND the "Flex" point at which the Trunk hinge impinges
on the Wiring Itself.
3.A bad diode in the Rectifier Bridge of the Alternator.

If it drains a healthy battery overnight it's a Big Drain (s).
I'm gonna throw out a WAG since I don't know the schematics of your chassis's
wiring diagram...It's an UnFused "Hot At All Times" user.

Invest in an inexpensive DMM from Sears or HF.
You need to know how bad the Amperage Drain is .

I had a battery killer once. We couldn't find the problem, until I went to the customers house, where the car was dead, and saw the brake lights on when I pulled up. The owner would shut off the car with the brakes on, and the car still in gear. Then, they would put it in park and release the brake pedal.

I ended up adjusting the brake light switch on this car.

It's time to disconnect things on the car... one at a time, until the light goes out, then troubleshoot what's out.

It can be a royal pain, but hopefully, it won't be a hard fix.

isolate the alternator - it can be quite a big drain when one diode goes bad. the brake lamps in a MB dont work with the key out, the bits that do work are the interior lamps, headlamps, parking lamps, trunk lamp.

There are some models that have two fuses behind the fuse box panel - I dont know what they are for, but cannot hurt to check them.

I only mentioned the brake light issue because in the case of my car, everything the ignition switch controlled had been monkeyed with... rather than just replaced the bad switch that was on the car.

My car was the KING of bad repairwork.

My alternator can be simply unplugged at the unit itself. Someone removed the little air duct and hose long ago.

Im not saying you are wrong, I did suspect that something must have been done to make them work without the key in order for them to work like that.

Right. No offense taken here, but I'm just throwing things out for the OP. His car could be as mucked up as mine was!!!

My 124 had the master relay causing this. It also caused the ASR light to stay on.

by master relay - you mean the over voltage protection?

Thanks. Keep it coming.
 

Lots of good thoughts here.
The drain is indeed big, since it kills a good battery overnight, and has the test lamp glowing at half brilliancy.

Alternator diodes sound interesting. Can I easily isolate it?

OVP relay? Again, can I unplug it? I think it is behind the battery.

I don't see any lights on overnight.


The car in question is my daily driver, 1995 E320s, with 202k on the clock. I throw two kayaks on the roof, twice a week, keep the paddler in the boot, and generally enjoy the car.
Thanks again.

I've got a 93 300D in that is doing the same thing. I'll check the trunk lite tomorrow. A couple more things is that when I start the car, as it is turning over, the interior overhead light flashes. On top of that the alternator that was in the car had bad diodes. You could measure resistance between each pole and the case of the alternator. Put a used alternator in it and it will charge but again, the battery dies overnight.

small update
 

Tonight I had the chance to remove all of the fuses for an extended period, one minute. Sadly, the test light never went out.

Midnight, by master relay, do you mean the OVP relay?

Disconnect your alternator next!!

Here is the amp draws I'm dealing with.
With all the fuses in it reads the highest - 5.6 amps.
With C fuse removed - 3.7 amps
With C and 9 fuse remove - 2.9 amps

I changed out the alternator with a used one that at least charges. Could it create a load on the battery like this and still keep the battery charged?

Another thing I am seeing is that with the key out, whenever I hook up the battery with all fuses in it immediately pulls in the A relay - power seat and F - power window relay.

Oh yea, did I mention that there are pecan shells all over the place in this car from the critters that have been living in it for the past couple years?

Yes. I had a brain fart when I posted that.

Do you have an after market alarm system?

They are in my opinion the worst of the worst for draining batteries.

Minor update.
 

No, to the aftermarket alarm.

What I am hearing, loud and clear from several sources, is alternator or OVP relay. I will try to isolate them and report back. Thanks for all comments.

Pulled the OVP relay
 

Test light no longer lit.
So, I guess it is the relay, or something that is powered by the relay but not fused.
I will replace the relay and report back.

I believe the OVP fuse is a 10 amp... red one.

I saw one in a parts car once that had a 25 amp fuse in it. I wonder if this had something to do with the car winding up at a junk yard?

One of the things that Scares me
 

Other Previous Owners (Idioten) "Improving" the Electrical System...
On Anything! That Drives or Floats.

Thank God you don't see so much of these Self-Anointed Rocket Scientists in Aviation !

First thing to suspect is the OVP. My 124 gave me fits with dead battery issues. Rain water got into the relay from the cracked rain gutter above the battery & cover for the OVP. R2'd the OVP & made a raincoat for it with a plastic sandwich bag & a twist tie. That ended the problem. The other issue is a fuse in an unpopulated holder. Check your fuse chart & if is suppoda be empty don't put on in there. Many years ago with mine, I installed a fuse in a holder that was not normally populated with the intent to carry another spare fuse. Big mistake. Be patient, you'll find it! Let us know how ya made out.

This is what happened to mine. It was like a swamp in it.

Overnight Battery Drain
 

No one mentioned the most likely culprit which I had on a 124. On the passenger side in the trunk is the radio amplifier. It shorts and stays on thus draining the battery. Hold your hand on it after it has not been in use for a while, if it is warm, there is your culprit.

OVP tomorrow
 

Thanks for the input.
If the rain breaks, I will install a new OVP relay on Friday.
Will let you know.

Is this a standard equipment item? Wouldn't this be fused through the fusebox?

It was the OVP relay.
 

As many here suggested, it was the OVP relay.
I just replaced it, and the test light in series with the disconected battery cable no longer glows.

Interesting note; besides input from this forum, I spoke to a knowledgeable tech at an MB dealer w/ a 30 bay shop. He said ' If you bring me a 124 with a problem, i am putting an OVP in it. If it is more than 6 yrs old,
it should be replaced.

very easy. open the hood to the service position. Remove the battery (negative terminal first, then one bolt in front of the battery at the base. Battery slides forwarde one half inch, and then will lift out.) Pull upward on the weatherstripping that is closest to the winshield, in the area of the battery, which holds the plastic cover behind the battery in place. The relay is a silver rectangle, approx 1 x 1 x 4"", inboard, with a fuse in the top of it. There are several different mounts. Mine came off just by loosening an 8mm bolt, not all the way. connecter just came off without any fancy hold-on clamps.

Also, the ASR light is now gone
 

after replacing the OVP relay.

Thanks to all who responded.