Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 79Get this manual
Engine Synchronizer Wiring Diagram Commander Gauges 1Wiring DiagramGauge needle to point toward
slow running engineTACHOMETER
TACHOMETER SYNCtiAONIZER
2Wiring DiagramGauge needle to point toward fast running engine TACHOUETER