Here are some common wiring color codes for Mercury and Mariner outboard motors that are listed in this chart:
Red: 12-volt hot
Purple: Ignition on key switch and gauges
Black: All grounds
Light blue/white stripe: Trim up switch
Light green/white stripe: Trim down switch
Brown/white stripe: Trim sender to trim gauge
Purple/white stripe: Trim "trailer" switch
Tan: Temperature switch to warning horn
Tan/blue stripe: Alternate color for temperature switch to warning horn
Yellow/Red Stripe: Starter solenoid to starter motor
Yellow/Black Stripe: Choke or Primer Fuel Enrichment
Yellow: Charging Circuit from Stator
Brown: Reference electrode MerCathode
Tan/blue: Audio warning buzzer
Gray: Tach