You will need to call the manufacturer, ZAPCO - 209-577-4268, or email them at tech support [email protected]
, in order to purchase the part you are missing. It is possibel to hard wire the RCA parts you need and creat a homemade fix, but in all honesty it is not worth it, and it will probably introduce a lot of interference in to the quality of your signal path rendering it a bad option. Give them a call / email. If they will only sell the part to a dealer, call Car Depot @ 615 - 269-8080 and they can have the part purchased and delivered to you for a small fee. Good luck.