Ignition Troubleshooting - 1978 700

[Berdink]

I have a 1978 Mercury 700.
130+/- compression.
I have spark on 1 and 3.
I have no spark on cylinder 2.
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I'm sure there are several methods of process of elimination.
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Here's what I'm thinking.
Let me know if this sounds right

Test 1
If there is Spark on 1 and No Spark on 2, swap the two trigger wires at the SwitchBox.
If spark returns on 2, and now no spark on 1, it’s the trigger.
If still no spark on 2, and there's still spark on 1, it’s not the trigger.

Test 2
If still No Spark on 2, swap the green wires going to coils 1 and 2.
If spark returns on coil 2, it’s the SwitchBox.
If still no spark on 2, it’s the coil.
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[Chris1956]

Sounds about right. Those older Mercs had issues with insulation falling off the wiring harnesses. You might also look for that.

CDI Electronics should make replacement components.

 

[Nordin]

Most of those Mercury and Mariner the switchbox fails.
From my experience the switchbox and stator fails, not so common with the trigger.

 

[Berdink]

Yeah, much looked good before I started touching things and the insulation started crumbling off the green corroded wires.
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I'll definitely be going through all the wiring and making repairs before I attempt to start it.
Same with the whole fuel system.
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