1993 240, 190k+ miles

The battery light in the cluster is barely illuminated when ever the car is running. The brightness never varies. And you have to have a eagle eye to see it, and only when it's dark outside. This has been going on for at least 6 months or about 3k miles.

I replaced the battery about 5k miles ago with an Interstate battery. It's still cooking along just fine. The alternator and all the big positive wiring from the battery to the starter and alternator looks good, some replaced, and connections are not corroded. It looks like someone replaced the alternator sometime before I bought the car about 2 years ago.

All the grounds I checked seem to be fine. I don't have other electrical problems that I know of. Everything works.

The car starts fine in warmer weather, but is sluggish in cold weather. The starter looks original, but that's another issue for another thread.

What could be causing this? Are there common causes or issues? What things should I troubleshoot and how? Any suggestions?

Thanks in advance?