Narva 7 Pin Round Trailer Plug Wiring Diagram. 7 pin large round plug/socket; 7 pin ebs round plug/socket; Narva Trailer Plug Wiring Guide from www.narva.com.au I looked at the wiring loom running to the break. 7 pin h/duty round plug/socket; Narva trailer plug 7 pin flat plastic 82141bl.