Well this one really has a bunch of us down in Georgia stumped. Working on an 02 C320 wagon that the battery draws down overnite. We pulled every relay and the alternator out of the circuit. We still have a large arc when connecting the battery that shows on an in line ammeter to be about 7 amps. Even pulled all known fuses 1 at a time. Battery shows proper specific gravity in all cells. I would appreciate anyone with Any suggestions to holler out.

 

Seems like a damaged wire somewhere shorting out!!

 

Does the car have power seats? The modules of that era are known for not powering down during sleep mode.

 

Thanks for the replies folks l. Car does have power seats. Will check. We have checked for pinched wires in the usual locations like the lift gate and the drivers side hood hinge area. We will look further. Thanks again.

 

Since removing fuses does not seem to break the circuit is it possible there is damage between the battery and the fuse board?
I'm not familiar with your car.....does it have 2 batteries?

 

Only 1 battery in the car. We cannot visually see the entire harness as it snakes through the car. I suppose there could possibly be an unseen chaff in the loom somewhere. The car has been babied and has never been in an accident. Thanks for the suggestion.

 

Is there anything in the car that doesn't function properly?
Is there a tow hitch with a socket for trailer lights?

 

Unplug your power seats. Its a well known problem.
https://www.benzworld.org/threads/di...bucks.1403233/

 

Constant 7amp draw?
definitely not the seats then

 

OP says they pulled fuses and relays....Wouldn't that have isolated seats at some point?
I'm inclined to agree that it's not the seats though it would be good to get to the bottom of the problem ( no pun intended)!!

 

Nope. It's crazy I know. Basically the seat modules have 2 power inputs. One which is fused and triggered by the ignition key and a second constant power input unfused only used for memory. The seat modules fail in such a way that they draw down through the memory power supply. Mine were actually staying warm over night so 7a draw is perfectly conceivable and they would murder the battery over night. The above fix is the correct solution.

 

I hope you are correct and this proves to be a solution.

 

The best (cheap and effective) way to fix this problem is to cut the constant power wire to the modules and wire it instead to an adjacent switched power wire which the module also uses. Nice and easy.

This kills the ability to adjust the seats while the key is switched off. However, the power seats will still work normally when the key is switched to position 1. See video below for reference.


Personally I don't have power seats, so I can't comment on the actual fix itself.

 

I went through this shlt with my 02 C320 wagon. When I bought the car the power seats were unplugged. I thought that was strange so I plugged them back in. Next morning battery dead. I did the above fix and no problems ever since.
Both the video and my link describe the same fix. Easy test is to simply unplug the power seats and see if your battery keeps a charge over night.

 

Power seats cannot draw so much. Its mcu issue that causes can bus to stay active.

 

Only 1 way to find out. Unplug the seat modules and see if the problem goes away.

 

So we cut the constant power wires going to both seats and left the switched wires intact. Now when we turn the ignition on we have lost power to the starter (wont turn over), lost power to the climate control panel, and the radiator fan goes into high speed mode as if the engine is hot and the a/c is on max. Indeed looks like the original thread title was spot on.---Crazy Electrical draw. Suggestions Anybody? Anybody?

 

You cut or unplugged? Where did you cut the wires? What wire colors?

 

I cut the wire that had 12v on it even when the key was off. Incidentally i found the problems that caused us to lose power to the starter and caused the radiator fan to come on by itself. Fuse 51 i think was in its seat cattywampus causing the fan relay to lose control and starter relay wasnt plugged in all the way. Pulling fuses and relays over and over hunting this draw down causing us to get a little sloppy in our work as we are at wits end with this vehicle. Owner states this has gone on a couple times for the last 2 years now. Now he tells us.

 

Ah geez. That would've been an easy fix. Better late than never I guess.

Since you've already snipped the seat module wires, you might as well complete the switched wire mod.

Is the power draw problem solved then?

 

The inline ammeter is showing no draw as of this pm. Waiting till tomorrow am to see if it is sneaky overnite and decides to draw by itself. This thing is possessed. Thanks for the reply.

 

Why cut wires when you can simply unplug it.

 

So we did the seat mod to drivers and passengers seat. Battery still drawing down overnite. Wondering if we may have a sticky relay, i have as of this afternoon pulled all relays in the car and set them aside. Gonna see whether the battery has drawn down tomorrow morning.

 

Like I said seat will never draw 7 amps unless you see smoke coming out of them!
so what is your current draw at this moment?

 

X