From the 1960s, these 8-pin rectangular connectors have been used to connect video monitors to VTRs. We've always known them as “Honda connectors,” presumably because Honda made the connectors used on these early machines.
They carry audio and video signals, in both directions: VTR playback to the monitor, and output from a TV tuner to the VTR (allowing recording of the station the TV monitor was tuned to, or from a stand-alone TV tuner).
Sony and Panasonic both used the wiring as shown on this page, yet Shibaden chose to use an incompatible scheme. And some 1980s computer RGB monitors choose to use this connector for their own purposes. If anybody needs these alternatives, and can't find them anywhere else, I'll have a dig through my old notes to find them.
The signal levels are usually the same as the individual video and audio input and outputs on the VTRs and monitors. I've never had any problems using a breakout cable between VTRs and monitors where only one of them had the Honda connector.
There are multiple ground pins on these connectors, each for their own purpose. Don't use the wrong ground, and don't join them together.
I update these pages from time to time, if you're returning after a long time, scroll through to see if anything has been added or corrected (last modified on 17 Aug 2020).