1999-2002 TRX400EX Fourtrax Service Manual, Page 245Get this manual
ELECTRIC STARTER STARTER RELAY VOLTAGE Disconnect the yellowred wire connector of the starter relay switchMeasure the voltage between the wire harness side connector terminal (+} and ground (-)If the battery voltage appears only when the starter switch is pushed with the ignition switch ON, the circuit is normal
OPERATION CHECK Disconnect the starter relay switch connectors and cablesConnect the fully charged 12V battery positiveterminal to the relay switch yellowred wire connectorterminal and negative terminal to the yellowgreen wire connector terminalThere should be continuity between the large terminals while the battery is connected, and no continuity when the battery is disconnected