Anyone know the functions of this circuit board?

Well, if you search that website......

https://eastcoastcircuits.com/Circuits

You might have to contact them, because it's a 100-3 and all the new boards they are selling are 100-4

Again, based on that website it's likely an LED controller to blink or sequence LEDs- however that specific function of the sequence or "what it does" is specific to the code flashed to the microcontroller chip. So they used one common board- and then programmed them for different functions.

I cannot see in your picture if the orange painted chip has any text on it indicating the program type.

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Again, the current series of boards says this- but unknown if that then applies to the older series 100-3

• Input 9-12V AC/DC
• Dimensions 1.70" X 1.70"
• Draws approximately 10mA

I would try a 9V DC battery as a test leaving the LEDs connected to the outputs and see what it does.

Thank you, Vernon. I will investigate further...and good eye on catching the manufacturer!

No text that I could discern on the orange chip. This is a Railking building and the former owner obviously went for flashy effects with multiple signs and who knows what else, however he did not care for the building, or was rushed to build a layout, that is evident by how he retrofitted it all together, made holes, and wired it. I've thoroughly cleaned the outside walls of the 4-story building...it was at terrible mess, and windows were installed upside down and not flush with frames, clumps of spackle paste slopped on just about everywhere; window acetate missing from about 1/3 of the windows, wind. Next comes the electronics. Even if they don't work, I'll get some warm lights installed and this will be a nice addition to my uptown city.  I have to admit I enjoy working more on buildings than the trains. Thanks again, Vernon.

Paul the wiring for the board is shown in the online instructions on the site. The product is RLC-1; for random lighting controller. It will turn on/off up to 6 separate random leds for varying times of 5 to 45 seconds. Yours appears to be wired for 3 leds only, so you can add 3 more if you so choose. And you are right; the red/wht wires are power.

Thank you, Rod.