no spark 1983 70hp

what should the voltage be on the bk/yl wire going to the switchbox. That's the wire with the mercury switch on it. I have 0 volt and 0 volt out of the key switch in the control box. I have jumper 12 v to that terminal on the switchbox and still no spark.

The black/yellow wire "coming from" the switch box is the kill circuit line. If the mercury switch (tilts) and completes the connection the voltage which would have gone to the coils is sent to ground. Likewise, there should be one or two other "branches" in the black/yellow - one to the kill switch or man overboard button on the cowl (if equipped) and one going to the harness to head up to the control or keyswitch.

The ignition on these does NOT work on DC until after the switchbox and it's considerably above 12 volts.

The stator produces upwards of about 360 volts AC that it sends to the switchbox. The switchbox converts it to DC and stores it in a capacitor (or a number of capacitors depending on the number of cylinders). The "trigger" tells which sparkplug to fire by sending an AC pulse to the switch boxes SCR (a relay switch) which then releases the stored DC in the capacitor to the spark plug coil. The coil up converts it to somewhat north of 85,000 volts (if I'm remembering correctly) which jumps the gap on the plug and lights up the mix in the cylinder.

You CAN NOT test the stator or trigger with a standard multi-meter, you need either a direct voltage adapter for the meter OR a direct voltage meter (DVA or DVM), not something that most guys have in the tool box.

There is NO WAY to test the switchbox so you have to test everything else in the system.

You can check the resistance of the windings in the coils (and the trigger and stator for that matter) to see if they have continuity or not, but that only tells you if the copper winding is intact and not if it's "leaking" (cracked housing) or producing the required voltage - and trying to hook up a meter to a coil looking for 85K volts is just asking for a bad hairdo

Someone will jump in here (I'm sure) with the exact link to either ebasic power or maxrules websites which have a step by step to test your ignition at home (at least to the extent you can) with a ohm or multi-meter...

OH , OH ----------The ignition system on your motor does not need the 12 volt battery in order to make spark !!----------You have made a serious mistake here by applying 12 volts to the black / yellow wire.---------The ignition system generates the spark from the spinning of the flywheel magneto.

thanks for the info so far. I am getting 420 v on that wire while cranking, 0v in run position Did I damage any thing by jumping 12 v. Last time out I noticed the volt meter was at 16v, was going to check that out and now wont start, are they related

You probably didn't damage anything. There are blocking diodes in the switch box that will guard against some stray voltages.

420 volts during cranking sounds fine if it's making it into the switchbox, through the rectifier and being stored for use by the coils - if it's bleeding out down your (kill) line to ground, the motor is never going to start.

And yes, the stator voltage should be on the kill circuit (black/yellow) just shouldn't be going to ground.

Having that voltage there is telling you that the stator is most likely doing it's job fine and your lack of spark will lie elsewhere - trigger or switch box itself - not usual to have both coils go floooey at the same time, but possible I guess.

I would test for continuity between the trigger leads and if it's there I would consider swapping the switch box.

But before I got that far, I would totally isolate that black/yellow wire - make sure it's not going to ground anywhere and unless you are a "believer" I would totally scrap that mercury switch - if you try and start a motor with it fully tilted in the trailer position, you deserve bad things to happen