Strange electrical issue with 2001 Civic

I have a 2001 Civic, manual, and I began experiencing an odd electrical issue, I’m hoping someone might have some insight. This is a bit long, so I apologize in advance.

Roughly a week ago, my battery light came on when I first started driving, as I let out the clutch. As soon as I was going, it went away. I assumed it was just because it was cold and the RPMs dropped as I was starting out. Everything was fine for my 35mile drive home. The next time I drove, I again saw the battery light on, except at the end of my drive, the light would come on every time I would idle or downshift – any time the RPMs would drop. When I pulled into my driveway this time, the RPMs dropped to about 500 and the car died. It started up again with no issue. I drove around a few more times, short distances, and the light would always come on when idle, but would shut off as soon as I started driving and got the revs up over about 2k.

At this point, I assumed it was either an old battery or just dirty connections. A few days ago, I pulled the cables off the battery, scrubbed the connectors and terminals with a wire brush, and reconnected the battery. I checked the battery and it was sitting at 12.4V without starting it… turned it on and there was no light. The next day, I started the car – no light – and let it warm up for about 10 minutes… when I came out, the light was on again. I checked the battery and it was still sitting at 12.4V. I had checked the voltage on the battery (car off) a few times and it was always between 12.3-12.5V, right where it should be, so I’m assuming the alternator is functioning properly. I decided to drive work, since it had only been an annoyance at that point.

About 15miles from home, the dash went dead… all the gauges shut down, radio shut off, heater stopped working, etc. Car still ran fine, however. I decided to turn around so I didn’t get stuck too far from home. As soon as I slowed the car down on the off-ramp, power came back to everything. I drove home with no issues except the battery light coming on again. I went to the store later on and the car was idling strangely. It would rev around 2k RPM, drop down to about 500, then settle in around 900, where it’s normal. It then began doing that while I was driving… when I would downshift to slow down, the engine would rev a bit and not slow as it should. That was the last time I drove it.

I’m going to have to look into it tomorrow before it snows again, so I was hoping someone might have an idea what to look for. I do plan to check the alternator at idle and at 3k, but because the battery is charging, I’m leaning away from that being the issue. The issues with the dash are making me thing it might be something closer to the cabin. Any help is greatly appreciated… again, sorry for the novella.

TIA