Nutone 80's door bell

I have an older mid 80s Nutone system. The main panel had to be removed in a remodel. I want to replace with a simple door bell (we never use the intercom - very poor) , but I can't seem to figure out which wires I need to connect to a simple bell. (All the wires - many pairs and threes are now exposed, but old panel is gone. Is there somewhere I can get a manual or is there a simple way to do this? Thanks for any help Mike

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