Battery Drain - PeachParts Mercedes-Benz Forum

-=DeanstuD=- · #1 09-04-2010, 09:24 AM

New battery died overnight, I guess I have a problem. I had this happen once before, and I noticed the rear door/floor lights would stay on even with the switch off. I removed the bulbs, figuring that should fix the problem... Well maybe it did, maybe it didn't. The battery apparently still has a draw since it killed a new battery overnight.

I didn't think it would fix anything, but it couldn't hurt, so I used a brass brush and cleaned all the fuses and connectors. I disconnected the + cable, and attached a test light between the + post and the + cable. With the ignition off it lit the light. I proceeded to remove/replace each fuse and relay until I found which one would put the light out. # 15 is the magic fuse, when I pull it, the light goes out. The card in the fuse box lid list it as;

Roof light rear - OK, goes on goes off.

Trunk light - I don't know where it is, and I have never seen any light.

Safety belt handover arm - No idea what this is. Automatic seat belt? For the coupe I guess.

Switch over valve seat back arrester - I have no idea what that is, and neither does google.

Central locking system- All the locks work.

Door lights - Front door lights work, turn on and off with the doors. The rear door lights, see above.

Reading lamps/rear compartment - These lights work with the switches. on/off

Autom. antenna - The antenna switch seems to work properly with all functions except going all the way up. It will go to half way automatically with the radio on/off. You can bump it up and down with the rocker, and you can turn it off. I did notice it was still up in the morning when battery died over night. I think it should have been down.

Control unit seat adjustment memory - seat memory doesn't work.

Trailer turn signal control unit - you got me.

I have read allot on the subject through various searches, but never is there a solution. Seems the answer is always just a miraculous automatically fixes itself, or there is no solution.

vstech · #2 09-04-2010, 09:28 AM

look in trunk for a frayed wire near hinge. also, unplug the antenna cable. these batteries are robust, no light left on overnight will drain it much. my bet is on the antenna motor failed. or a serious frayed wire shorting out.

zeke · #3 09-04-2010, 09:57 AM

antenna may be the problem - seems to be drawing power in my 300TD that is having a similar problem.

bobodaclown · #4 09-04-2010, 10:57 AM

I'd also keep an eye on the central locking system (door lock pump). I think it's in the back seat. Have you done any work in the trunk? Might have knocked a hose connector loose. You've trouble shot it down to the fuse. Now track it down to the component. You're honing your trouble shooting skills. You could unplug each item to see what is causing the problem.

TX76513 · #5 09-04-2010, 11:03 AM

How is your antenna seal? If bad water can seep n store in the Hirchman antenna shorting out and drawing power. Some Hxxx atennas have a drain that can clog.

sixto · #6 09-04-2010, 12:24 PM

The three things I see that aren't bulbs are the central locking pump, antenna and memory seats. Continue with the test light test disconnecting each of these devices. The central locking pump is wrapped in foam to the right of the spare tire. It can function normally even if it gets stuck in a continuous loop. Each front seat has a bunch of connectors under the forward edge. Slide the seats back and raise the forward edge. IIRC some connectors can be interchanged so mark them before removing.

I believe the seat back arrester is a feature in an SEC's front seats.

Sixto
87 300D

-=DeanstuD=- · #7 09-04-2010, 09:42 PM

I unplugged the antenna which had one plug, the door lock motor in the trunk which had 2 plugs, and 3 plugs from each front seat. The light remained lit.

I put a multi--meter in place of the lamp, and it shows the amp draw fluctuates between .70 and .74.

Any other ideas, or are there more plugs I missed?

sixto · #8 09-04-2010, 10:07 PM

My info says the security system is also tied into fuse 15. Remove the front carpet and false firewall. Locate the long box with Becker markings. Remove both connectors; about 12 pins each IIRC. See if you still have the draw.

Sixto
87 300D

sixto · #9 09-04-2010, 11:06 PM

Maybe there's a bad switch in a visor so it's on all the time.

Sixto
87 300D

Palangi · #10 09-04-2010, 11:20 PM

Quote:

Originally Posted by sixto

Maybe there's a bad switch in a visor so it's on all the time.

Sixto
87 300D

Happened on me on my 123 300D. The glue that holds the mirror unit in place starts to let go, allowing it to open far enough to turn on the light. If you're troubleshooting outdoors during the day, you probably won't see it, especially if the battery is already low.

-=DeanstuD=- · #11 09-05-2010, 03:53 AM

Quote:

Originally Posted by sixto

My info says the security system is also tied into fuse 15. Remove the front carpet and false firewall. Locate the long box with Becker markings. Remove both connectors; about 12 pins each IIRC. See if you still have the draw.

Sixto
87 300D

Passenger side? I have seen a couple of posts on a Google search referring to security on that fuse also. I was just going by the card in the box.

There are no lights on in the interior, as I have just come home from my parents house tonight and it's all dark inside. I will tear the carpet out of the front passenger side tomorrow, as I think thta must be the correct side.

Searching more and reading and reading, I am feeling like the fact the rear floor lights were always on would be my problem. Here is my thought process about why it is not the problem.

I am assuming that if there is no bulb, that there is no drain from them. Also I am assuming that if the problem with the lights is that some wire has rubbed off and shorted somewhere, then it would pop the fuse, not just drain. Is that flawed thinking?

sixto · #12 09-05-2010, 01:20 PM

There can be a stage in which corrosion or some material acts as a weak conductor. Enough to draw power below the setpoint of the fuse.

Sixto
87 300D

-=DeanstuD=- · #13 09-07-2010, 12:33 AM

Quote:

Originally Posted by sixto

My info says the security system is also tied into fuse 15. Remove the front carpet and false firewall. Locate the long box with Becker markings. Remove both connectors; about 12 pins each IIRC. See if you still have the draw.

Sixto
87 300D

Sadly, I removed the carpet and false firewall, and the security system was already unplugged.

Interesting note. When I went out to work on the car again after a day or two, I hooked up the test light and it was off, no drain. I removed and replaced the #15 fuse, and then drain was back again. I would then remove the fuse and it would wink like 5 to 10 times (not randomly) and then go off. I would replace the fuse, the light would be on. Remove and it would wink. Over and over you could get it to do the same thing. Maybe I can capture it on video or something...

sixto · #14 09-07-2010, 12:40 AM

The devices on the circuit probably do a self test or something like that whenever the battery is reconnected. Such as to ensure the antenna is retracted or the central locking pump lock/unlock selector is in a neutral position when you remove the key. That's not unusual in a *ahem* modern car.

Sixto
87 300D

Murkybenz · #15 09-07-2010, 02:35 PM

I read a post whilst searching the net a few days ago concerning battery drain.

This was on a w124,the owner checked for days on end and got nowhere until he locked the car whilst checking.

He had a relay about an inch square beside comfort relay under rear seat that was drawing power,with the car locked then if he relocked without unlocking the power drain ceased.

I have searched hard for the thread but cannot find it.

His car had the comfort windows up and down on door key function but it had ceased to work at the time of battery drain.