Here's my radio distribution box. There are two output looms made from white Nyvin, a four cable one at the front and a two cable one you can just see at the back.
This is what the four cable one looks like:
They feed a pair of boxes marked "Mod RJB", one near the commander's shoulder and one underneath the engine fire extinguishers. Here's the latter:
I suspect, but haven't yet checked, that on each RJB the incoming power is on the side socket and there's probably a pair of terminal strips inside feeding the cables that come out through the grommets. Just pop the cover off, connect to the terminal strip and off you go!
Andy