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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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio