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Old 12-05-2016, 12:32 PM
martureo martureo is online now
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Join Date: May 2010
Location: DC Metro/Maryland
Posts: 15,936
Electrical gremlins

1984 300D, mostly stock

Battery is 3 years old, MBZ. Alternator is 5 months old, 3rd replacement (several reman defects in a row) in less than a year. 65 AMP Bosch.

At idle my DMM reads 14V. With headlights with highbeams on, heater on full, radio on, rear defroster on, and brake pedal depressed, I still get 12.75 V. Raised idle brings it back up to around 13.5V.

I haven't load tested the battery, and it may be part of the issue. Glows and starts without hesitation every morning (daily driver). But I've noticed my driver's headlight is rather dim (stock, Bosch sealed beams). If I hit the high beams the driver's headlight goes out completely. Additionally, sometimes after a long cold night, after driving for a few minutes, hitting the brakes will shut the radio off and dim the headlights/dashlights quite a bit. Seems to act like there's not enough power in the system, but will shut off and start up no problem.

Any clue as to where to start (after load testing the battery)?
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