Mystery wiring harness clamp | IH8MUD Forum Nov 09, 2016The attached pictures show a broken plastic clamp that held the main wiring harness against the right side of the firewall on my '95. Two local dealers have showed me that the clamp does not appear in their parts diagrams. They swear on a stack of FSMs that the clamp must be an aftermarket add-on to my truck. Mystery Wiring Harness | Diesel Truck Forum - Oilburners Jul 27, 2017Hello all. Has anyone ever encountered a wiring harness plug like this? It's a long thick wire like a 7 way but it only has 3 wires in it that i have concluded are trailer brake, back up light, and auxiliary. It runs from the floor of the cab (89 f350 cab and chassis) to the rear of the frame.