Mercury 75 OptiMax Owner's Manual page 123

OUTBOARD INSTALLATION
SMARTCRAFT HARNESS CONNECTION
If SmartCraft gauges are being used with the outboard, route the
SmartCraft wiring harness through the grommet and connect it to
the SmartCraft harness connector on the engine.
a
23700
a - SmartCraft harness connector
WATER PRESSURE TUBE CONNECTION
If a water connection to the engine is required for a water
pressure gauge, make the connection as follows:
113
eng