how to troubleshoot kill/ignition switch merc '90 115hp o/b

joeboater7

Cadet
Joined
Apr 23, 2012
Messages
27
Motor was working great 1 minute, next minute wouldn't start. Turns over strong, but zero spark.
 

Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
28,420
Disconnect the black/yellow (killer) wire at the switchbox, or at the ign switch. If spark returns, that wire is being grounded somewhere to kill the spark. The insulation can rub off and ground it.
 

joeboater7

Cadet
Joined
Apr 23, 2012
Messages
27
Disconnect the black/yellow (killer) wire at the switchbox, or at the ign switch. If spark returns, that wire is being grounded somewhere to kill the spark. The insulation can rub off and ground it.
OK, will do. That's very helpful. I did a test yesterday I saw someone online recommended.. I disconnected the black/yellow from the switchbox and checked voltage between it and ground and saw zero(0), but when I turn the ignition key to run position, and checked volatage between the black/yellow and ground, it read .4 volts. I think that is bad, right?

So my key ignition is built into the shifter box. Would that be the next place to disconnect? I mean, is the issue between the ignition switch and the motor, or could it be some other element on the motor itself given the .4 volt reading?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,420
The stator feeds voltage to the switchbox. It sounds like time to ohm out the stator. A Mercury Factory service manual is your best choice.

BTW, voltage on the black/yellow wire is bad.

If the stator ohms out OK, the switchbox is the next possible culprit.
 
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