Flashing Defrost and seat heaters
 

in all the years of owning countless W124's I have never experienced the following.

yesterday, as some of you may know, GA and the south east was hit by a pretty severe snow storm. So, logically, the wife and I decided it would be a grand time to be out and about. well upon entering the car (1995 E320 wagon, 148K), the car was started and as per standard cold-weather operating procedures, the seat heaters and rear window defroster were activated. then they began to flash. looking down at the console it was as if a wig-wag pattern had been activated. then the rear defroster switch also started to flash. eventually they resumed normal behavior and as far as I can tell all electrical functions are normal.....but what the heck was that! :confused:

I think the high-drain accessories automatically cycle or shut off temporarily if the voltage in the system is too low. It says that in the owners manual. Might have been your issue. Too much load on the alternator at low-rpms so you had voltage drop. Seat heaters + rear window defroster + the car's ignition system + fan etc....is probably well beyond the low-speed output of the alternator.

When they flash like that, it means the car has temporarily shut them off to conserve power. My E320 did that once, it was an extremely cold morning. It doesnt mean anything is wrong persay. I have a brand new heavy duty Interstate 93 series battery. They resumed fine when I started driving. But yes, it is rare to see...

Easily remedied by simply installed a higher output alternator when the time comes to replace it.

I wouldn't worry about it if it were freshly started and idling, the accessories are consuming more than the alternator can output at idle and therefore the alternator has not yet recharged the battery from starting the car. Normal. My TE did that from new if you were sitting idling in traffic long enough.

that sounds right since yes, it was super cold, and yes the car was just started. very interesting. these 124s have all kinds of behind-the-scenes secrets. like I said, first time in around 10 years of various 124s. cool :D

May be time to replace the voltage regulator and the integral brush assembly..
Inexpensive part, about $30 and takes about ten minutes to install.