Mercury - Diesel Mechanical Helm Harness Non-DTS Helm Wiring Interface 84-8M0084296. This Mercury Diesel Mechanical Helm Harness is designed for installations using traditional non-DTS control systems. It serves as the primary helm-side wiring interface, organizing and transmitting electrical signals between helm components and the diesel engine system.. Built for durability in marine environments, the harness supports straightforward mechanical helm layouts without digital throttle and shift fe