For what it's worth, I had the same symptoms on my 82 300D a few years ago when the alternator failed. For some reason, the BAT light did not come on when it failed, but all the idiot lights on the left side would not come on in "test" mode when starting the car. I thought it was an instrument problem until the battery went dead. When the alternator was replaced the lights worked normally again. I assume the alternator had some unusual failure mode that did not cause the BAT light to come on (an internal short maybe?).

Did you say your alternator had stopped charging when this happened? It's not that unusual for rebuilt alternators to fail right away. I would test and/or exchange the alternator and see if the light issue fixes itself.