I recently needed to convert a Sega twin unit arcade machine that had model 2 boards to one that used model 3 boards. I found it really difficult to find information on which pins do what on the filter boards so to get my head around how to change the wiring I made my own diagrams since none seemed to exist.
Model 2A, Model 2B/2C and Model 3 all use the same connectors for everything except for power. the only difference is the connector locations. The power connectors that have a line through them are for output; typically used to power another board somewhere.
If you find any errors in these please let me know.