Pagoda SL Group
W113 Pagoda SL Group => Electrical and Instruments => Topic started by: Philippe VIARD on May 14, 2025, 13:16:12
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Hello,
Please help me understand the following problem:
I charge my battery with the ground wire completely disconnected from the negative bushing.
when the trunk is closed (open circuit at the trunk light bulb) and I open one of the doors, the door opening indicator and/or brake level indicator lights up very weakly at the instrument block!
What do you think?
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Hello, as you know, removing the earth strap from the battery effective opens the circuit from every electrical appliance and lamp in the car. I can only think that maybe your battery is leaking, creating a circuit down to ground under the battery, have you removed it to have a look underneath? You could also measure on a low DC volt scale, and see if you get a reading between +ve and ground, with the earth strap removed
Out of interest, what's the significance when you say, "when the trunk is closed"
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Thank you Bobh for your answer.
My finding appears only when the battery is charged with an external charger.
The ground cable of the car is disconnected and isolated when I use the external charger.If I remove the charger from the vehicle, the anomaly disappears. This eliminates a battery leak to a mass.
The closed rear trunk means that the trunk light is off
ps: my car is a french 280sl from 1970
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Hello, i can't think of any other reason. Connecting your charger will boost the battery voltage, which, if it is leaking would exaggerate the problem, easy enough to test, by lifting the battery out and inspecting it, or using the voltmeter. Unusual problem on a car, i agree, but relatively common with lead acid batteries in fire and security alarm systems. If you insulate the battery from any metalwork, then it will also rule it out as the cause
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I removed the battery and found that there was no battery runoff on the support plate.
I did not charge the battery for 24 hours. I did not observe the abnormality (low-light brake lamp) that justified my observation.
The measurements made between the positive pole of the battery and the chassis (earth cable removal) are 9.3mV closed trunk and door open or not.
I see that this value tends to decrease over time. but increase again if I charge the battery
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Do I remember correctly that the French cars had this safety cut off installation. Do you have it? Can it be related?
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Which security device are you referring to?
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Again, I may be pointing your attention to a completely wrong direction, if so, I am sorry:
https://www.sl113.org/forums/index.php?topic=38568.msg281636#msg281636
https://www.sl113.org/forums/index.php?topic=32842.msg239152#msg239152
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Hello,
Please help me understand the following problem:
I charge my battery with the ground wire completely disconnected from the negative bushing.
when the trunk is closed (open circuit at the trunk light bulb) and I open one of the doors, the door opening indicator and/or brake level indicator lights up very weakly at the instrument block!
What do you think?
Every appliance and lamp in the car requires a +ve and a -ve (ground) to operate
Your door open/low fluid level lamp has a +ve connection to the battery via the switches and fuse, but if you've disconnected the ground wire at the battery it won't have a -ve connection and therefore cannot light, it simply does not have 12V at the lamp, even with the battery charger connected. I think the fact that you first noticed it when the charger was connected is misleading you
So, if it does not have a -ve to complete the circuit, where is it getting a voltage from?
Does your trunk light illuminate when you open it, with the earth strap disconnected?, i understand that this should have a permanent feed, ie it operates without the need for the car lights to be switched on, so in theory this should also show dim at the same time as the door open light
I'm still of the opinion that the battery is leaking and causing a small current to find its way around the circuit, has your door open lamp been replaced with an LED at any time?, this may explain why it's illuminating dimly, it may only need a tiny voltage/current to light up, whereas other lamps will need a decent voltage to light up, even dimly
I would still try insulating the battery completely from all metalwork, remove the clamps, and stand the battery on insulating material, a rubber mat or similar, or simply try and hold the battery in mid air and simulate the problem
You seem to be having to charge the battery regularly?, perhaps it is failing internally and it's time to replace it
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Thank you Bobh for your involvement.
Battery in charge, negative strap disconnected and isolated, trunk open (door open or closed) the bulb filament does not blush.
Yes I replaced the incandescent bulbs of the instrument block with LEDs last October, which may explain why I had not noticed the anomaly before.
As soon as I have found an insulating plate, I will put it under the battery and I will do the tests again.
My battery is constantly charged by a charger-tester type Optimate because I use my vehicle rarely .