As you've figured out by now, funky lights and jumping tach in a W124 (or W201) means a low battery and no charging which is about to leave you stranded. GET GENUINE BOSCH PARTS FOR THIS! Yet another lesson I learned the hard way when the local shop replaced my 300E's alternator 3 times in 6 months. You guessed it, I was stranded 3 times, once 100 miles from home.
99 E300 TurboDiesel
00 Jetta TDI