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Old 01-16-2005, 06:31 PM
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Join Date: Jul 2003
Location: BC, Canada
Posts: 109
1989 300E Electrical Load & Alternator

I was driving my '89 300E at 100 km/hr (2700 rpm +/-) in -18 deg C (-1 deg F) when I noticed that the seat heater indicator light was flashing. According to the manual this means that the electrical system was overloaded and therefore the car automatically shed this load. I was very surprised as the car has a year old battery and I thought that the rpm would be sufficient for the total electrical load required (std lights on high beam, rear window defroster, heating fan, and whatever else the car requires for normal running). The seat heater was at the low setting.

I switched off the rear defrost and the seat heater stayed on (low setting) but the seat indicator light started to flash after turning the defrost back on. The other observation was the head lights and dash lights dimming slightly when I turned the rear defrost on.

I'm a bit dismayed as cold weather does require all these loads and shedding one for the other doesn't make the car more comfortable. I didn't even have a passenger for the other seat to add further load. I wish I had a voltage meter in the car so I could observe voltage fluctuations while switching these device on and off.

I did some searching on this and it appears that the pre '90 300E's had a 70A alternator that were less than optimum for heavy electrical use and in 1990 MB installed 80A alternater that also had better low rpm capacity.

Is what I observed "normal" behavior or do I have some underlying problem? (ie - alternator brushes?) The car has about 180,000 km (112,000 miles) on it.

Thanks in advance,

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