Engine Wiring Harnesses for Mercruiser Sterndrives 14-pin to 10-pin (new style) wiring harness adapter plug. Required when replacing pre-2006 Mercruiser engines with a 2006 and later complete Mercruiser engine package Adapter allows you to connect 14.. Mercruiser wire harness. Motor harnesses. Engine harness Wire Harnesses There are two basic types of harnesses. One is the Motor Harness and the other is the Instrument or Dash Harness. The Motor Harness is the harness that is on the engine. It typically connects the starter, alternator, senders and ignition components together.