Here is a photo of mine, and it is the junction box for the radio. My car was ordered without a radio but came with the "kit" to install one which I did myself. The wire to the radio was hidden in the loom so I ran my own (the brown wire) to the radio and the jury rigged static suppressor. I also rewired the fog lights and power antenna and they are also hooked up to this box. I did this 45 years ago and I couldn't begin to tell you how I figured it out back then:-)
John