- Fig. 1. Simplified schematic diagram of a typical trim-tilt circuit wiring on an outboard engine.
- trrimWiringDiagram.jpeg (40.41 KiB) Viewed 2632 times
I will describe how the circuit operates.
LOW CURRENT CIRCUIT
The negative pole of the coil or solenoid of each relay is always connected to the battery negative. The positive pole of each relay coil is connected to separate poles of momentary-contact, center-off rocker switch for UP or DOWN operation. When neither UP or DOWN positions are pushed, the relays are not energized.
When the UP pushbutton switch circuit is actuated, the UP relay coil positive pole is connected to the battery positive, current flows in the coil, and the UP relay armature changes to the NORMALLY-OPEN circuit.
When the DOWN pushbutton switch is actuated, the DOWN relay coil positive pole is connected to the battery positive, current flows in the coil, and the DOWN relay armature changes to the NORMALLY-OPEN circuit.
Note that there can be more than one switch controlling the trim relays. A second switch can be wired in parallel.
Often the relay power is provided via the ACCY circuit from the ignition key switch for the trim switch at the helm. This circuit is usually fused with a 10-Ampere fuse. This circuit only has power when the ignition key switch is in the ON or RUN position. The trim switch at the cowling is typically powered directly from the battery.
HIGH CURRENT CIRCUIT
The trim motor circuit is connected to the two relays at their COMMON terminals. When neither relay is energized, both BLUE and GREEN motor leads are connected to the battery negative terminal via the UP and DOWN relays at their NORMALLY-CLOSED contact. The trim motor does not run.
When the UP relay is energized, the motor's BLUE conductor is connected to the battery positive via the UP relay's NORMALLY-OPEN contact. The motor's GREEN conductor remains connected to the battery negative terminal; this causes the TRIM motor to run in the direction that raises the engine.
When the DOWN relay is energized, the motor's GREEN conductor is connected to the battery positive via the DOWN relay's NORMALLY-OPEN contact. The motor's BLUE conductor remains connected to the battery negative terminal; this causes the TRIM motor to run in the direction that lowers the engine.
Typically there may not be a fuse in this high-current, or if there is the fuse, the interrupt current value will be large, perhaps 40-Amperes.
Note: the conductors to the UP relay are marked with blue insulation or blue-white insulation because blue is the color of the sky and the sky is UP. The conductors to the DOWN relay are marked with green insulation or green-white insulation because green is the color of the earth and the earth is DOWN.
If automotive-type "Form-C SPDT" relays are used, a very odd numbering system is used to designate the terminals. The following table can help explain what relay contact is indicated by what numbered terminal:
30 = relay contact COM
85 = relay coil negative
86 = relay coil positive
87A = relay contact NORMALLY CLOSED
87 = relay contact NORMALLY OPEN
Another wiring diagram shows the configuration using these numerical terminal designators at is shown in Figure 2.
- Fig. 2. A typical trim circuit with the relay terminal indicated using numbers.
- trimCircuitRelayWithAutoContactNumbers.jpg (98.7 KiB) Viewed 2632 times
Boaters who have little understanding of electrical circuits and who poke around or tinker with electrical circuits often cause more harm than good to the circuitry and the components of the circuit.
Any electrical circuit where there is a direct connection to a battery with large diameter wire has the potential to create a serious short circuit, very rapid heating, and destruction of components in the circuit. Be very careful when working with 12-Volt circuits connected to a very large storage battery. The stored electrical energy in a large 12-Volt storage battery can be very dangerous.