Also check the black and yellow wire connected to the key switch.
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Mercury/Mariner Standard Outboard Wiring Color Code
Color Where Used / Function
Black All Ground
Brown Reference Electrode MerCathode System
Orange Anode Electrode MerCathode System
Lt. Blue/White Stripe Trim UP Switch
Lt. Green/White Stripe Trim DOWN Switch
Brown/White Stripe Trim Sender to Trim Gauge
Purple/White Stripe Trim "Trailer" Switch
Gray Tachometer Signal
Black/Yellow Stripe Shorting or Stop Circuit
Pink Fuel Sender to Gauge
Red Unprotected Wire from Battery
Red/Purple Stripe Protected (Fused) Wire from Battery
Red/Purple Stripe Protected (12 Volt +) to Trim Panel Control
Purple Ignition (Switch) to 12 Volt Positive
Tan Temperature Switch to Warning Horn
Tan Temperature Sender to Temperature Gauge
Tan/Blue Stripe Temperature Switch to Warning Horn
Yellow Starter Solenoid to Starter Motor
Yellow Starter to Regulator (Charging Circuit)
Yellow/Red Stripe Start Switch to Start Solenoid to Neutral Start Switch
Yellow/Black Stripe Choke (Enrichener System)
Green with Color Stripe Switch Box to Coil - Striped and Numbered
White/Black Stripe Bias Circuit (Switch Boxes)
The ABYC Recommended Colors
Color Where Used / Function
Yellow/Red Starting Circuits
Brown/Yellow or Yellow Bilge Blowers
Dark Grey Navigation Lights & Tach Signals
Orange Accessory Feeds
Brown Pumps
Purple Instrument Feeds
Dark Blue Cabin and instrument Lights
Light Blue Oil Pressure
Tan Water Temperature
Pink Fuel Gauge Sender