M3 convertible 1999 electrical issues w locks and heat console

A few months ago I noticed one of the interior light switches stopped working but ofncourse this couldn't be replicated when I took car in for service. Then the heating system began shutting off intermittently, with the display disappearing too, and buttons for fan and other controls not working either. It comes back on within about 5 or 10 min. Now the locking and/or alarm system is totally whacky - remote key doesn't work half the time and sometimes when it does, all the doors unlock again. This also happens when I lock the car with the key.

This all seems worse when it is very cold outside.

The battery is a year old, and car is in great shape otherwise with 88k miles.

Thanks for any suggestions u might have.

There have been reports that the wiring harness that runs along the trunk have caused such issues. I would suggest that you check the trunk arm wiring harness for any internal broken wiring which might cause this.
If you do a search you can find many write ups with pictures showing the damage.
This would be about the easiest thing to check...