Abstract: A subassembly electrical isolation connector for interconnecting adjacent tubular drill rods of a drilling system used in drilling bore holes in earth formations electrically isolates the inner connection of the drill rods. The connector comprises a housing, a mandrel, a connector for connecting the housing to a first tubular drill rod, a connector for connecting a mandrel to a second tubular drill rod and a device for interconnecting the housing and the mandrel in a manner to electrically isolate the housing from the mandrel with the housing overlapping at least a portion of the mandrel. The housing has an isolated end which is electrically isolated from the mandrel and the connector for connecting the mandrel to a second tubular drill rod. The mandrel has a conical tapered body portion which is located within the housing and the housing has a corresponding conical tapered inner surface. The conical taper for the housing and the mandrel converge inwardly away from the housing isolated end.