I have a 1989 300E. The problem I am having is when I am driving at night I turn my lights on and they work fine but I noticed that the lights go bright then dim then bright again. This is not only the head lights but the interior lights also.

What could be the problem?

Thanks

Fab

Most likely an alternator/charging problem.

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How do I test the alternator?

Thanks

Fab

Could this also be caused by my serp belt slipping?

Thanks

i have the same problem with my 87 300e and its probably a weak/bad alternator, ive never had a charging problem so i ignore it (i know the little battery icon light works on my car) it could also be something with the voltage regulator but its hard to tell without swapping out for another one. i would think v belt slippage would manifest in other ways long before being able to cause a problem like this. do the belts squeal loudly even when the car has warmed up? some nice battery chargers have the option to test alternator and your local parts store will probably do the same for free (still haven't learned how to use my multi meter but im sure it would test it too) hope this helps!!

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Although the dimming lights would seem to be evidence enough of a problem with the charging (alternator) system, try this test that my F-car mechanic taught to me.

Go down to your local RV supply house and buy one of those plug-into-your-cigarette lighter, digital voltmeters. I say your local RV place because they seem to be the cheapest place to buy these things. Should be around $10.

Plug it into your cig lighter with the car powered up, but with the starter NOT engaged. You should have a reading of just over 12 volts. Start the car and with the car in idle, you should have a reading of between 13.2 and 13.9, but not over. Drive around town and keep track of the readouts, especially when the lights go dim. Check it again when you turn off the engine. Readings that don't go over 12 when the car is running would be a problem with the alternator. If they read in the 13 range when running but less than 12 with the engine off would seem to indicate a problem with the battery.

Let us know what you find.

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I will try this out on the weekend and post my results.

Thanks,

Fab

typically a 25 dollar voltage regulator fixes the issue

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1994 e320 Cabriolet 108k



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I finally checked out what voltage my car is putting out when I am driving the car.

When the engine is off the voltage reads 13.25 volts

When the lights are dim the voltage reads 13.22 - 13.61 volts (this is when the car is on and driving)

When the lights on my car are at their brightest the voltage reads 17.77 - 18.02 volts (this is also while driving)

Now to me this would be the voltage regulator. The cheapest I could find was $75.00. The dealer wanted $96.00. So before I buy it I wanted to make sure that this was the problem or do I need to change the whole alternator.

Thanks

Fab

Can anyone out there help?????

Super,
This is from experience on a much less sophisticated vehicle, but I'm going to throw it out there and hopefully get some interest flowing:

First, 18v -period- sounds too high to me.

My experience started with a bad battery (stored and sulfated) that was no longer accepting a full charge (voltage ok), so that my electrical system was all but running directly off of the generator (yes generator), which messed up the voltage regulator (overworked) multiple times (as well as a stereo aplifier x 2).

My only point would be to make sure and check out the condition of your battery if you don't know already for sure, as to prevent going round-and-round as I did.

It's that 18volts that makes me think that this may be a possibility. Scotz

Thanks for the reply ScotzBenz. The battery is only a year old and when I put my volt meter to it, it was well over 12V. Is there another way to test the battery?

Thanks

Fab

Check price of voltage regulator here at Fast Lane.

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1993 190E 2.3
2000 Toyota 4x4 Tundra

Click on "buy parts" on top of this page. Two screws an you are done...

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'86 300E

Unfortunatlly fastlane does not ship to canada.

Thanks