The Roadmaster 6-Diode Universal Wiring Kit for Towed Vehicles with Separate Lighting # 154-792-118158 does need to be grounded to the vehicle chassis at both locations. Without a solid metal to metal ground, the converter and the trailer wiring may not function properly. It is possible they could work being tied together and connected into the towing vehicle ground through the 4-way wiring harness, but that is putting a lot of faith in your tow vehicle ground connection and the gauge... view full answer...