CL500 2004 - Electrical issue preventing car starting

[Parkheadlad]

Hello. I have a very frustrating issue which is steadily getting worse. Can I apologise in advance for the long description below but they may provide clues for any electrical wizards out there. I bought my CL 500 just under a year ago and it came with a parasitic draw on the battery. As a consequence I have always disconnected the negative strap from the battery when parking up to prevent the battery going flat. This has not been a problem until recently (last couple of months) - when I connect the negative strap to the battery in most cases there is no response to any of the electric within the cabin and the key will not turn in the ignition. Up until a couple of days ago, I solved this problem by repeatedly removing and replacing the negative strap and eventually for some reason the electrics are restored and the engine starts no problem. The battery is relatively new and fully charged throughout. Now things are getting worse - this morning I removed and replaced the stray about 15 times with no effect. I then connected jump leads to my other car's battery ( without starting the car) and it started no problem ( even though the battery in my Merc is fully charged). And to finish off, later today the car cut out while at a set of lights ( causing havoc) which has never happened before. I managed to get it going again when I used a spare battery to jump start the car (after removing both negative and positive straps from the battery a couple of times)- but once again the Merc battery is fully charged!!
To date, I have asked 5 auto electricians to source the problem but they have not been interested - they say the electrics in the Cl500 are to complex and are not prepared to take on the task. One of them said it could be a loose earth wire somewhere?
Another strange thing I found out when I connected the negative strap and got no response was to check the battery voltage. When I attached the clips from my voltmeter to the positive and negative electrodes of the battery I got a reading of 12.2 V BUT when I attached one clip to the positive electrode of the battery and the other clip to the securing bolt of the negative strap I only got 4.2V??? I have no idea what is going on!! I am losing patients and confidence in my Merc and desperately seeking advice/ suggested auto electricians in the West Cumbria area. Any help will be gratefully received.

 

[Larkone]

Is there a break in the negative lead because of the continual movement? Do a resistance reading on the cable between the battery connection and the securing bolt. How old is the battery? Does it have an auxiliary battery and what is the condition of that?

 

[peterws1957]

Have you checked each circuit at the fuse box to see which is causing the drain. (plenty of youtubes to show you how to do this). See if there is any sign of corrosion in the SAMs. Then I'd be checking the output from the alternator which should be producing 14.4 volts with engine running. I would have thought that a good MB indie with Star would be able to diagnose what's happening.

 

[Parkheadlad]

Hello. I have a very frustrating issue which is steadily getting worse. Can I apologise in advance for the long description below but they may provide clues for any electrical wizards out there. I bought my CL 500 just under a year ago and it came with a parasitic draw on the battery. As a consequence I have always disconnected the negative strap from the battery when parking up to prevent the battery going flat. This has not been a problem until recently (last couple of months) - when I connect the negative strap to the battery in most cases there is no response to any of the electric within the cabin and the key will not turn in the ignition. Up until a couple of days ago, I solved this problem by repeatedly removing and replacing the negative strap and eventually for some reason the electrics are restored and the engine starts no problem. The battery is relatively new and fully charged throughout. Now things are getting worse - this morning I removed and replaced the stray about 15 times with no effect. I then connected jump leads to my other car's battery ( without starting the car) and it started no problem ( even though the battery in my Merc is fully charged). And to finish off, later today the car cut out while at a set of lights ( causing havoc) which has never happened before. I managed to get it going again when I used a spare battery to jump start the car (after removing both negative and positive straps from the battery a couple of times)- but once again the Merc battery is fully charged!!
To date, I have asked 5 auto electricians to source the problem but they have not been interested - they say the electrics in the Cl500 are to complex and are not prepared to take on the task. One of them said it could be a loose earth wire somewhere?
Another strange thing I found out when I connected the negative strap and got no response was to check the battery voltage. When I attached the clips from my voltmeter to the positive and negative electrodes of the battery I got a reading of 12.2 V BUT when I attached one clip to the positive electrode of the battery and the other clip to the securing bolt of the negative strap I only got 4.2V??? I have no idea what is going on!! I am losing patients and confidence in my Merc and desperately seeking advice/ suggested auto electricians in the West Cumbria area. Any help will be gratefully received.

Hello. The battery is only 10 months old. The

Is there a break in the negative lead because of the continual movement? Do a resistance reading on the cable between the battery connection and the securing bolt. How old is the battery? Does it have an auxiliary battery and what is the condition of that?

View attachment 82305

Hello. The battery is only 10 months old. The negative battery strap have clean connections and secure but that is my focus today - to remove it and check it for breaks. I'm having the Merc MOT'd on Thursday so will ask them to check the alternator - any idea if the CL500 provides easy access to the alternator ( not that mechanically minded). Thanks very much for the advice - will keep you updated.