Just went through that on a 89 260e and a 88 300te, both have the same problem, a bad diode in the recitifier. In other words, replacement alternator time. The bulb prove out for the IC in the 124 cars is done through the diode trio in the alternator, the ABS and SRS are powered differently. This is why you keep the ABS and SRS prove out and loose pretty much everything on the l/h side of the cluster. However, I've seen them still light the oil level sensor bulb and I had one that the oil level light stayed on that was eventually traced to the alternator.
BTW, if you can get a retrofit for a 90 amp, do it.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.