The wiring of the sensors and controls on a diesel engine in a boat involves several design variables, including:
- engine manufacturer preferences and choices,
- mechanically injected vs. electronically injected common rail technology platform,
- “normally-open” vs. “normally-closed” fuel shutoff solenoid,
- manufacturer and package options for gauges/sensors
- transmission neutral safety switch variables, and
- transmission oil pressure and temperature sensors/gauges, if installed.
The propulsion engine on Sanctuary is a Cummins 4BT-3.9 mechanically injected engine with a normally closed fuel solenoid that requires full-time DC power to keep it open. The OEM sensor/gauge package is manufactured by VDO and includes tachometer, dual station oil pressure and temperature gauges and audible alarm sounders. We installed dual station aftermarket high exhaust gas temperature sensors and alarms.
For those owners who perform DIY engine maintenance and repairs, I have included the wiring diagram I prepared for Sanctuary. For simplicity, this diagram DOES NOT show gauge illumination wiring. Click the following link to get a downloadable Adobe .pdf copy of Sanctuary’s engine wiring diagram: 20161022_engine_room_instrumentation_terminal_block. This engine has two different kinds of oil pressure and temperature sensors. The set that feeds the oil pressure and temperature gauges is analog. The set that feeds the safety alarms is bi-modal (“on”/”off”).
Although this drawing is specific to the Cummins 4B, I would think it is “typical” of what would be found on many engines. I encourage all boat owners or develop a wiring diagram of their propulsion engine. If you ever need it, having it will save the skilled labor cost involved in figuring it out, diagnosing failures and making repairs.