Battery Drains

[AAR]

Hi,
I am seeking for an advice and help    the battery gets drained almost in 1 year, twice.
Alternator was changed on September along with the battery. (Battery Bosch 12v70Ah).

But again before 2 days, the battery again got drained, and got it changed.

- The car didn’t start on P
- The car started and engine got running on Neutral
- When I changed to Reverse, the car stopped working and needed to switch it on again.
- On gear 2, i noticed it was a bit cranky, moving but it seems it will stop anytime.

Any advice.

[dirkbalter]

I think you should start evaluating the start stop switch and insure its working correct.
https://www.sl113.org/wiki/Automatic/Start

[Cees Klumper]

If you do have what's called a 'parasitic drain' that depletes your battery, a common method to find the culprit is to hook up your multimeter at the amp draw setting, then remove one fuse at a time until you get to the circuit that draws the power. Then you have narrowed down where it could be.
My Pagoda has an alarm system that takes a certain amount continuously and will deplete the battery if left connected. So rather than hooking up a battery charger for the roughly 7 months I am not near the car, I have a quick disconnect switch that totally cuts the battery from the car.

[lpeterssen]

Dear friends

Please note that the only fused circuit that has power while the car is on the off position is fuse no.1…..

Therefore the only accessories that may deplete a battery are:

1. Cabin light
2. Glove box light
3. Clock
4. Or any other load attached to a T30 line or directly at battery.

In my experience our friend AAR has a defective tired, exhausted main wiring harness that has compromised insulation on main T30 lines, specially on the engine bay area.  Those lines as written on many post have a cotton resin insulation that is prone to cracking after many years of being exposed to elements (heat, water, oil).  A T30 line with compromised insulation will cause a parasitic draw form battery, and that can not be avoided by removing any fuse, since those lines per design have no inline fuse on them.

Therefore my advise is to replace that harness or make it serviced by someone with know how on that.

Best regards
Eng.Leonardo Peterssen
Www.wiredoktor.com

[merrill]

hello
it could be the battery,

in my 78 300d I had 2 MB batteries with internal issues.

after replacing the defective MB with a new MB battery and then chasing what i thought was parasitic draw i gave up (because i could not find it) and went to a walmart battery and the problem when away.

[Pawel66]

I am not a mechanic, but what seems to me:

1. Battery going flat and starting/stopping as you described may be two different topics.
2. On the battery
- unless you have late US car with 55A alternator, your battery is probably too big, it should be 55AH, not 70AH - may never be properly charged and will die
- charging while engine running and illumination of charging control light should be checked (lit when ignition on, off when engine running), charging voltage with engine running close to 14V
- then, if the above is checked and fine, I would look for drains as described by other Members; the way I did it - hooked multimeter in series and removed fuses one by one

3. On starting and stopping: it would help if you describe a bit - was engine cranking but not starting or not cranking? Is it manual or automatic? Does it have CSD to control idle with gear or it is an US version? If the car was cranking and not starting - I think it is a separate issue from the battery issue.

[AAR]

Thanks for the advice, I will be mentioning this point the expert working on the car, although he also advised to add a battery disconnect switch.

[AAR]

The mechanical working on the car adviced the same method for the battery.

[Pawel66]

Yes, battery ground cut-off switch is a very good idea for our cars if they are enjoyed occasionally. I have one.

Please note that clock is the device that works all the time when battery is connected. It is not supposed to consume a lot of energy, it uses it just for winding, but if anyone „repaired” it in the past and did not use proper thermal fuse protection, it may be a small ticking bomb.

Ground cut off, being a very good idea, is, however, more like concealing symptoms rather than fixing the root cause in case of drains.

[lpeterssen]

Ground cut off, being a very good idea, is, however, more like concealing symptoms rather than fixing the root cause in case of drains.

I cant not agree enough with Pawell statement.

I was going to say exactly that.

If you have a battery drain scenario and you install a battery cut off switch you are treating just the symptoms and not the root cause of your car illness

It will solve the surfacing problem but you have a serious situation underneath that may lead into an unfortunate car fire that will destroy your lovely toy

Better to address the root cause than to cry later

Best regards
Lp
Www.wiredoktor.com

[lpeterssen]

Dear friends

Another solution if you are allergic to a major main harness intervention solution would be to install what I have named PATCH HARNESS.

That harness runs in parallel to your original one and addresses what I have observed in many years as being the common failure points on MB w113 50 years old original harnesses.

With this patch harness that sell for only 385$ you can be confident that the battery drain will go somewhere else

See this link:

https://wiredoktor.com/products/mb-w113-charging-system-upgrade-and-patch

Best regards
Lpeterssen
Www.wiredoktor.com

Of course I personally prefer the approach of servicing the full main harness at least

[lpeterssen]

Hi,
I am seeking for an advice and help    the battery gets drained almost in 1 year, twice.
Alternator was changed on September along with the battery. (Battery Bosch 12v70Ah).

But again before 2 days, the battery again got drained, and got it changed.

- The car didn’t start on P
- The car started and engine got running on Neutral
- When I changed to Reverse, the car stopped working and needed to switch it on again.
- On gear 2, i noticed it was a bit cranky, moving but it seems it will stop anytime.

Any advice.

Regarding the car only starting in neutral but not in parking,  you should check the neutral/parking reverse switch at the firewall. Disconnect it from the rod that mechanically links it to the transmission. Maybe the rod needs to be adjusted in length

Best regards
Www.wiredoktor.com

[Ed Riefstahl]

Here is a super simple and super fast trick I learned as a mechanic back in the 70 to check for a battery drain, especially if you're working alone.

Remove the key from the ignition and shut all doors and trunk. Disconnect the negative cable from the negative battery terminal. Clamp one end of a 12 volt test light to the negative battery terminal and touch the other end to the negative cable. If it lights up, something is either open, turned on or, shorted.

To find out which circuit is the culprit, simply remove one fuse at a time, (usually starting with clock) until the light goes out. Yep, you can use a voltage meter too. This trick lets you wiggle wires or play with glove box light switch etc. while you watch to see if the light flickers or goes out.

I'll bet I've used this trick a hundred times over the years I'll bet. Thanks Paul! This guy taught me so many things I've used for 50 years. Wish he was still around.

Happy motoring!
Ed Riefstahl

1966 230SL (Ms Magoo)
1970 280S (Miss Daisy)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - One of 1000, (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5