Mishimoto 2003-2004 Ford 6.0L Powerstroke Glow Plug HarnessGlow plug harness failure is quite common for high mileage 7. 3L and 6. 0L Powerstroke models. Although many owners will find this harness damaged while performing other engine maintenance, sometimes a hard cold start is an early indicator that the harness has begun to fail. Years of supporting high amperage glow plug draw combined with high engine bay temperatures will melt the plastic connectors, eventually resulting in shorts within the circuit.