W169 2008 A Class 150 Petrol Manual Lights Issue -

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New Member
Aug 21, 2021
Dartford Kent
W169 MB A150 Classic
I have an issue whereby my car had been suffering from a drained battery. The battery was replaced recently with a like for like new Varta battery which worked for a time. It became obvious that there was a type of unseen drain on the battery. This meant the vehicle would quickly develop a flat battery which required jump lead starting. If the vehicle was used daily the problem was not apparent. Recently I took a holiday and had asked for a family member to run the vehicle to ensure the battery and vehicle were OK. It was reported the battery was flat. The family member was asked to use jump leads to start the vehicle (big mistake). They had no experience of this and I presume they crossed the polarity. This action partially melted the Positive post and completely destroyed the jump leads. The battery however, appears to work correctly. Upon return I attempted and successfully started the car from new jump leads. I took the car on a run but it became obvious there was an issue with the lighting. The front lights, along with the nearside rear running light stay lit even though the light switch is set to off. The vehicle is considered undriveable as the brake lights do not operate - dangerous for other road users and somewhat illegal. The indicators, horn and interior lights work as normal. As a precaution I removed the festoon bulbs from the front cubby and boot area as this may have caused the intitial drain due to a faulty pressure switch. The cab interior festoon bulbs remain. I ran an OBD2 check for error codes. None were found on the basic device I used. There are no dash error codes. I have checked the low amperage fuse array individually. I have not checked the 3 other 60 amp fuses that show in the battery compartment array. None of the low aperage fuses were shown to have fused. When locking the car, a short period elapses and then the front lights - headlamps, side lights and fog lights go into what I can only describe as strobe mode. The rear nearside running light also strobes. The offside rear light cluster does not light up during this event. All bulbs on the offside have been checked and found to be sound. Importantly, the radio does not operate but the blower, on all settings, does operate. Normal cabin heating is apparent. The AC has never worked and this I understand is due to a faulty pipe MB fitted to this and some other MB models of this era - an irrelevant issue in this context. The front wiper and screenwash operate correctly, as does the rear wiper and screenwash.

When locking the vehicle from the keyfob, all locks function as expected. A short time will elapse and then the strobing effect previously mentioned, will happen. When an attempt is made to unlock the car from the keyfob, there is no activation. The only way to gain entry is to use the manual, physical key in the driver's doorlock. When opened the alarm activates. When the keyfob is placed in the ignition the alarm resets. To show the problem in realtime I have uploaded a video.

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I cannot afford to visit MB or an independent. I understand their STARS diagnostics may isolate the problem though. From the research I have done it is entirely possible a relay may have been partially or entirely destroyed. Worse, the ECU or SAM unit may also have taken a hit. If this is the case then I will give strong thought to scrapping the car as the expected exhorbitant costs would not be justifiable. This would be my last option as the car drives perfectly and I would like to ask other members if they have any pertinant suggestions.

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