RIM Electronic EQ Module

I bought this strange looking eq module and have been trying to figure out what the pin connections are as there seems to not be any info online about it. The only thing I could find is this page https://www.radiomuseum.org/r/rim_stereo_equalizer_ems_rkl.html which doesn't tell me much.
From what I can tell from looking at the board it looks like pin 0 is ground, pin 1 is input or output, pins 2 and 3 are input or output and pin 4 is a power rail.





Anyone familiar with these?


EDIT: I've had another go at this and figured out the pinout.

0 - GND
1, 1' - Left and Right input
2, 3 - Left Outputs
2', 3' - Right Outputs
4, 4' - V+

I don't know what voltage it was designed to run on but will probably work on 12-30v.

I still have a Radio Rim catalogue from the 80s. They contain most schematics. If you send me a pm as a reminder I can have a look at it when I´m back at work.