I had to slide a four pin connector much larger than 3/8 for my fog lights. I did it through the common wiring harness grommet. I taped it to a Philips screwdriver, after silicone spraying it. Was fine. I did it all the time when I I stalled radios.
You may of course amputate RCA plug and reattach or attach a new one. Many years ago, I'd prefer USA-made Switchcraft brand for good performance and not too bad pricing. Parts Express offers many choices now. HTH.