no spark

[rawdawggs]

I just purchased a 1986 35 hp Mercury outboard SN-0A988236. It had no spark, mech said to change the switchbox(I did) still no spark. I disconnected the black/yellow kill wire and still got nothing, I then disconected the yellow wire from rectifier, Still no spark. I even disconected the 8 pin plug from thr motor and tried to do a manual start. Whats next?

 

[verado7]

Re: no spark

stator - usually

 

[achris]

Re: no spark

You need to get/make a DVA meter (peak voltage) and test the system methodically, not just 'shotgun' it.

Theory of ops for a Merc ignition system.

Referring to the following diagram....

The stator (under the flywheel) has 2 sets of coils, a high speed set and a low speed set. These generate a voltage of 250-400 volts. The switchbox/es rectify this power and store it in a capacitor (inside the switchbox/es). the trigger coils also live under the flywheel and generate a small (2-8v) signal as another magnet passes it. When the switchbox/es senses this signal it discharges the capacitor across an ignition coil, depending on which trigger was fires, and whether the signal was positive of negative.

Last but not least, the battery charging circuit has absolutely nothing to do with the ignition system.

Understanding HOW the system works is paramount to being able to troubleshoot and repair it.