The slave solenoid is usually located on the same bracket as the breaker on the engine. Look for the big red button most likely on a bracket near one of the exhaust risers....the slave solenoid is near/behind the breaker.
However, the slave solenoid is momentary and only activated when your ignition switch is in the start position. If your engine won't shut down, the cause is more likely to be a bad ignition switch rather then the slave solenoid.
