Hi, im jake and recently I bought a 1989 E320 coupe and it was working ok and in mint condition. A month pass by and I encounter a problem. When I switch on the headlights my battery drains out therefore I cant use my car during nights. Pls. help me so I know were to seek help and whats wrong with my car. Thanks...
My alternator was changed back then but still encountering power drain when I turn on the lights.

Most likely your have a voltage regulator problem. The voltage regulator is attached to the back of the alternator and is easy to replace. If you have a volt meter, check the voltage with the headlight off and then on. You should have about 13.5 volts. If less then 12 volts, the battery is being drained.

Thanks, Can I do it on my own or should I see a mechanic?

Sure, you can do it yourself if you can get your hands on a 0-20v DC digital voltmeter.

Set the selector dial to the 20 volts DC scale and attach the red lead of the voltmeter to the positive (+) side of the battery and the black lead to the negative (-) side. A fully charged battery should read approx. 13.2 volts DC. Have a helper start the engine and raise the idle to about 1500 - 2500rpm. The voltage should climb to 13.5 - 14.5 volts. Check again with the headlights on, should be about the same, maybe a little lower. If the reading is 13.0 volts or less then the charging system is not doing it's job. Since they replaced your used alternator with another used alternator it's difficult to tell if the problem lies with the alternator or the regulator without bench testing it, although I would agree that it's most likely the regulator that's at fault. And you still don't know the condition or age of your battery. A battery will generally last between 3 and 6 years, and doesn't usually give a lot of warning before it dies. You might consider doing the basic voltage tests yourself, post your findings here and then take it to the shop and have the battery charged and then load tested and the alternator/regulator tested for charging output level.

The voltage regulator sells for between $24 and $34 from FastLane and is pictured below. It's very easily removed from the alternator to check the brush length or replace the unit. You can see the regulator mounted on the back of the alternator at the 6 o'clock position in the 2nd picture below.

Hope this helps

Gary

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Thanks a lot gary, you really are a great help. Anyway il try to check it first for myself and if things get tough I'l see a mechanic. Now I remmeber the owner of the car told me that he just recently replaced the battery but unforetunately the car was not used for about 4 to 6 months before I bought it. And another thing when I release my gas pedal I feel a jerking movement behind and I think its coming from the newly replaced brake pads (not a genuine parts), but Im not quite sure. Can you tell me whats wrong with my car? thanks again..

Jake,

I'm afraid I can't tell you what's causing the jerking movement based on what you've described, but I think I can say that it's probably not caused the new brakes. There are a number of quite good aftermarket (non-genuine MB) brake pads that work just fine, and none that I can think of that would, in and of themselves, cause any kind of problem like the one you're describing. If you can give a more complete description of the symptoms it would be helpful in determining what some of the possibiities might be.

For example, by "jerking" do you mean a repetitive forward and backward motion that the whole car goes through as if there's a big rubber piece in the driveline that is flexing and unflexing, or perhaps just a slight pause followed by a "clunk" and then a feeling of decelerating?

In regards to your battery, you might want to consider doing the following:

Go to Sears and buy an automatic battery charger, a couple of those felt corrosion inhibitor rings that go on the battery posts, a battery terminal brush and an automotive battery hydrometer to test the specific gravity of the electrolyte. Try to find one that has a glass tube inside of a glass or plastic bulb syringe and reads specific gravity by numbers, such as 1.280 for fully charged, 1.240 for 75% charged, etc. If Sears doesn't have one, check any auto parts store or on the web. If your battery is the sealed type, i.e. it doesn't have removable vent caps on top, don't worry about the hydrometer. I would also recommend buying a BatteryMINDer (About $40). In addition to keeping the battery fully charged at all times you can also use it to keep power applied to the the car's electrical system when you disconnect the car's battery for charging. If you lose all power to the car for more than a few seconds you may lose some stored electronic information, such as the radio code.

If your present battery is not a sealed type, carefully remove the top caps and see where the water level is. It should be right up to the bottom of the hole. There's usually a slot on one side of the hole and when the electrolyte level reaches the bottom of the slot you can see the liquid surface suddenly change from flat to radiused at the edges. Use only distilled water to fill the cells, if needed, and do not overfill. Before filling, tip the battery to one side slightly, lift it about an inch or so and tap it on the bench (or wherever you've got it sitting) to loosen any trapped gas bubbles under the plates inside that might make it look fuller than it is.

After filling, use the hydrometer and check the reading. If it's less that 1.280, put the battery on the charger, following the instructions that come with it, until it indicates full charge. Be sure to check each cell individually, as they can vary depending on the condition of the plates in that cell. Also, keep an eye on the temperature. During charging the battery temp may rise as much as 25 deg. F. If it's much more that that, it may indicate a charge rate that's too high or possibly a shorted cell. Another reason for checking specific gravity of each cell periodically.

Initially, the charge rate may be quite high, upwards of 8 to 10 amps. This should taper off to about 4 amps within a couple of hours and down to as little as 2 amps toward the end of the charge cycle.

During charging the battery can release bubbles of hydrogen gas which is very explosive . Don't let any sparks or open flames come within 5 ft of the battery. These bubbles can also cause the electrolyte level to rise, so the "tipping and tapping" routine should be done every several hours.

The full charge cycle can take as long as 8 to 12 hours. After charging, let the battery sit for several hours to cool down. Once it's finished, wipe off any liquid electrolyte that may have collected on the outside of the battery, being aware that it contains sulfuric acid. Even a drop on your cothing (especially cotton jeans) will leave a nice little hole next time you wash them. Wear rubber gloves to protect your hands and immediately wash any part of your skin that comes into contact with it with lots of water.

Reinstall the battery in the car, clean the battery posts and cable terminals with the terminal brush, install the corrosion inhibitors and attach the cables, positive (+) cable first, negative (-) cable last. Start the car and recheck the charging system to make sure that you get 13.5 to 14.5 volts at the battery terminals.

The BatteryMINDer leads can be permanently attached to the battery and plugged into the BatteryMINDer whenever the car will be sitting for an extended amount of time, or as often as you like. It can't hurt the battery, only help it last longer. I've been using several on my cars and motorcycles for a number of years now with excellent results. It works especially well for the deep cycle battery in my little pop-up camper, which doesn't get used for months at a time and then gets used for 5-7 days straight without charging.

Hope this helps.

Gary

P.S. - Here's a link to the BatteryMINDer Owner's Manual . It gives a good description of how it works and some general information on charging flooded lead acid batteries (your typical car or motorcycle battery). Also, I've dealt with BatteryWeb.com several times and would recommend them without hesitation. I have no connection with them other than being a satisfied customer.

Hey Jake,

The most likely things would be an old, dying battery or a faulty alternator regulator or diode board. But first, how about a little more info, such as:

Was the battery recently inadvertently discharged? If so, what were the circumstances?

You say the alternator was replaced recently. Why? Was the regulator replaced at the same time?

How many miles since the replacement? Was this a new, used or remanufactured unit?

Who did the work, an indie, a dealer, or ?

Did they thoroughly check the charging system after installing it? What were the results?

Did they offer any warranty?

How many miles on the car?

Has the battery ever been replaced? Batteries often have a sticker that shows the month and year the battery was put in service. What's the date on yours? What brand and model is the battery in the car?

Do any dash warning lights come on when you turn on the headlights?

Any evidence of auxillary belt slippage such as squealing, or a shiny, slick surface on flat side of belt, or excessive belt deflection?

For quick, cheap check-up take the car to your local Sears and have them do a load test on the battery and also test the charging system. Many stores will do this for free or a minimal charge. They may also provide you with a printout. But don't buy anyting on their say so just yet. These aren't the most comprehensive tests, but sometimes they can point out a weak area.

Post your results and go from there.

Gary

Well with regards to all of your questions, I can only answer some. The batt was discharged once, and when they changed the alternator(2nd hand) I dont know if they changed also the regulator. Anyway you have given me info bout my car definetly I'll go to a garage for thorough check up. Thanks and Godbless...