Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 117Get this manual
Engine Synchronizer Wiring Diagram LIGHT BULB POSITION A
Wiring DiagramGauge needle to point toward slow running engine
Use this position when using separate light switch for instrument lighting!GRY=GRAY
WHT=WHITE
BLK=BLACK PUR=PURPLE
a 51105+12 Volt Light Switch WirePosition Light Bulb to the Unswitched Position
Tachometer Starboard Engine Synchronizer Gauge Tachometer Port Engine Synchronizer Module
Wiring DiagramGauge needle to point toward fast running engine
LIGHT BULB POSITION B
Use this position when instrument lighting is wired directly to the ignition key switch(Instrument lights are on when ignition key switch is turned on
GRY=GRAY