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Author Topic:   Ignition Key Switch Effect on Engine Spark

dan m posted 01-26-2011 09:55 PM ET (US)
[Inquired about ways in which the ignition key switch could affect engine spark]
jimh posted 01-26-2011 10:45 PM ET (US)
Typically there is a circuit in the key switch which suppresses ignition spark. You may want to identify the conductors associated with that circuit, temporarily disconnect them, attempt to start the engine, and thereby determine if they are influencing the problem. For some help with the key switch wiring, see
http://continuouswave.com/whaler/reference/ignitionSwitch.html
The diagram shown is for an OMC engine, but I suspect that a Mercury key switch will be wired in a similar fashion. Also, the conductors for the spark kill circuit have rather high voltage on them, and they may be arching over somewhere in the wiring harness. You may want to try to disconnect them at the engine end of the harness.
Check the safety lanyard, too.
The simplest way to rule out the ignition switch kill circuit as a factor will be to disconnect it at the engine end of the circuit. Do this as your next step. If the missing spark problem is not affected, the ignition switch was probably not the problem.
[Thread closed in SMALL BOAT ELECTRICAL.]

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Author	Topic: Ignition Key Switch Effect on Engine Spark
dan m	posted 01-26-2011 09:55 PM ET (US) [Inquired about ways in which the ignition key switch could affect engine spark]
jimh	posted 01-26-2011 10:45 PM ET (US) Typically there is a circuit in the key switch which suppresses ignition spark. You may want to identify the conductors associated with that circuit, temporarily disconnect them, attempt to start the engine, and thereby determine if they are influencing the problem. For some help with the key switch wiring, see http://continuouswave.com/whaler/reference/ignitionSwitch.html The diagram shown is for an OMC engine, but I suspect that a Mercury key switch will be wired in a similar fashion. Also, the conductors for the spark kill circuit have rather high voltage on them, and they may be arching over somewhere in the wiring harness. You may want to try to disconnect them at the engine end of the harness. Check the safety lanyard, too. The simplest way to rule out the ignition switch kill circuit as a factor will be to disconnect it at the engine end of the circuit. Do this as your next step. If the missing spark problem is not affected, the ignition switch was probably not the problem. [Thread closed in SMALL BOAT ELECTRICAL.]