Re: Electical trouble shooting
That is a 1987 Mercury/Mariner (so just a 20 Merc painted grey).
A single cylinder not firing after replacing the coils is "most likely" the switchbox.
Two "unfortunate" points about the switchbox - first, it retails for about 180 bucks so you don't want to swap it and see - second, there is absolutely no way to test it.
You prove it's the switchbox by proving everything else is working.
Since you have replaced the coils, that leaves the trigger and stator which "should" be tested before dropping almost 2 bills on a switchbox.
Simple tests can be done with an ohm meter.
I will assume you have an early stator, so if the colours I give you aren't there, drop back for a different version.
From under the flywheel, going to the switchbox you should have a black/yellow, black/white, brown/yellow and brown wires (amoungst others).
Between the brown/yellow and brown wires (trigger) you should have minimal resistance - almost total continuity - if you have NO continuity (tons of resistance) your trigger is toast.
Next test the stator - the black/white and black/yellow are tested one at a time.
Again you are looking for "minimal" resistance. If you have no continuity, the stator is toast.
Red lead to black/white and black lead to anywhere on the engine block (ground)
and then swap and test the black/yellow.
I expect both of these to check out good, but then at least you are fairly certain your switchbox is toast....
