My 300SEL has been very reliable, but I started to leave today and its acting funny. It started fine (its 21° here - well below average for us!) and it started missing and the dash lights were getting dim and bright, dim and bright (my taillight out warning light was on). I shut it down. I am thinking it sounds like my battery may have a poor connection.... I had a bad connection awhile back and it would start to stall. I may not have it tight enough... does this sound like it may be the case? I just came back in and decided not to go - and my Lexus dont like to go on slippery roads. Too cold to deal with it today... any suggestions?

Either alternator (voltage regulator) or battery issue.

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Thanks. Well, it cranked really fast when I started it. It has a Mercedes battery thats not very old, but its pretty cold here. Only about 21°, which is really cold for us. The battery light wasnt on, but it sure was starting to miss and the lights were getting bright and dim as if it was not getting a steady flow of power. It did fine for about two minutes as I let it warm up, then it started missing and the lights started fluctuating.

I tell you its always something with one of my cars, but at least this ones been OK until now. I was hoping it was a simple loose connection.

Just came in from the cold. I checked the connections and they seem tight... really tight.

The car was fine when I drove it on Sunday and its never gave a problem.

Voltage regulator - would the battery light be on if it was bad? How hard is it to change the voltage regulator?

Thanks.

Check if the battery cables have corrosion.

Thanks... they looked OK, but I guess I need to disconnect them and look at them and maybe go ahead and clean them. Its so darn cold though.... guess I could bundle up. Seems like when it drops below 25° my cars go nuts. Thankfully it dont often get that cold here, but this week has been terrible.

If you have a volt meter then you can take some readings and post and maybe get a diagnosis. You would want to measure the battery voltage at rest (car off), at idle, and at 1500 or so RPM. Also you can check your connections by measuring the voltage from one side of a connector to the other. For example from the clamp to the post. You would want some load to make some current so you could turn on the lights to do that test. You could do that test with the car off.

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Two screws hold the voltage regulator to the back of the alternator. It's a simple DIY job to replace. If the voltage regulator brushes are worn down to nubs it's time to replace it because the battery will not recharge properly.

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Fred Hoelzle

I had a similar sort of problem with all the warning lights .Replacing the Voltage regulator solved the problem .
The OVP relay will cause a similar symptom if the solder joints inside require re-soldering .Best to replace it at this stage .
stumbling and poor driveability is also caused by the voltage problem .it will sort itself when the voltage is stable

mak
300se

Take your DVOM and set it to AC and connect to a good ground and the positive side connection from the battery. Start and idle the vehicle. If you get anything more than 50mV (.05V), replace the regulator (or diode set if available & cheaper).

I just fixed a non-mb this weekend vehicle that had a 350mV 'ripple' that didn't set off the battery light and gave the same symptoms.

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Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Thanks. Well, I dont have any of those testers/gauges, so I simply removed and cleaned the terminals on the battery and cables. Presto, it didnt do it again (stumble and lights dimming/brightening) and it ran perfectly today. I am thinking this was the problem, because I had an issue in the summer when it was like I was losing a connection and it would start to stall. I think my cable ends are worn out.

Anyway, I guess it could still be a tiring OVP relay. It did kinda stumble like an old diesel when first started for about 15 seconds, but its usually not as cold here as it has been for the past few days, so I am experiencing things this car (and my others) dont do unless its bitterly cold. It was only 25° here when this was occuring, so I would hate to live where it gets below 0°, or I would be in trouble. lol. For now, all seems OK again.

Its also good to read that the voltage regulator is so easy to replace! Thanks for that Ferdman!

Thanks again.