The red and orange wires could be Battery Live and switched similar to the "Standard" that is in place now.
Or looking at the rear of one on ebay:
The sticker on the orange is for the power antenna.
If yours is similar to this then the the red/black on the right is your ground and power source. Orange is to power the antenna motor, so no you wouldn't tie the red/orange together. The rear mounting stud could also be used as a ground source.
Old timey days some manufacturers used the antenna wire as the ground path as well. A quick way is to use a DVOM and measure resistance from the Case to the Black wire. The orange as well should be a possible short or 0 Ohms to the red wire when the Radio dial switch is on.
VW did some of the older Cabriolets as well as beetles to have the radio's power on a Battery live, (unswitched) so that you could listen to the Radio when the car wasn't running. I got stranded once waiting for some one at the airport as I left the Radio on in my Cabby with the volume turned down, and didn't realize it till later... Which is why I changed it over to a switched source. Radio off when the key is out.
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