Hi again Rod,
Just had a thought. The radio in my Indiana is branded "Bailey". I would expect your JVC item to be similar, but worth while checking before buying lead.
One other tip. I also use these radio "LINE IN" connectors to couple my TV/SAT receiver sound through the caravan speakers. In my case, the cable I use for this is a "Twin Phono" to "Twin Phono" lead, 3mtrs long, again from Maplins