Yes, you can indeed use the ZCI Circuit Protected Vehicle Wiring Harness # 119250KIT to combine the tail lights on the semi. We actually recommend this product quite frequently for this purpose. To install the actual RV 7-way use install kit # ETBC7 which will include everything to install the 7-way and a brake controller. For a brake controller I recommend using the Tekonsha Prodigy P3 # 90195 since it is their most user-friendly and durable controller.
You may need additional wire and... view full answer...