78 Mercury 402 won't start

Made some welding repairs to hull, but forgot to pull the harness off the motor; now engine won't start.

I have replaced the Switchbox as the original had a 1 ohm ground on Kill lead coming from switch box after welding.

Also found plug on top cylinder had shorted between electrode and collar with metal that deposited after welding- this scraped off easily and plug was returned to service.

I get a nice spark outside of engine from plugs, but engine won't even spark with Ether.

Here are my Ohm reading on components, which all seem to check out per SELOC manual

Stator : Red to Blue terminal 5.9K Red to ground 51.2 Ohms

Trigger : between leads 850 Ohms

Ignition coil: Primary terminal .4 Ohms / Secondary to ground 1K Ohms

Here's my DVA readings.

Stator: 38V/308V with rectifier disconnected 31V/296V with Rectifier connected

Trigger: 1.5V across leads / .7V each lead to ground.

Ign Coil: Primary at Positive terminal to ground 220V top cylinder and 207V bottom cylinder

Not sure what a good test would be for the output of the Ignition Coils and I am stumped as to what else could be the matter.

I'm not familiar with a 402 but since you replaced the switchbox, are you sure you don't have the coils cross wired?

Thanks for the thought Mike. The wiring from the switch module is such that the wires are of different lengths to reach the the correct coil pack. I did find that I had the polarity wrong on the first cylinder and corrected it.

I've been able to get the motor to backfire now, but not actually start. I'm thinking the timing must be off.

JMichael My humble apologies! You were right!!! I found I had the output of coil one and two flopped when I checked the motor with a timing gun. A million thanks!

If you're just landing here from the Internet, here's the recap: I welded a pontoon without disconnecting the wiring harness from the motor. The result was a fried switch module. In parallel, I had replaced the carb float as it was half full of gas/oil. I checked all ohm values and DC values to isolate the motor not starting. The switch module was replaced and all other values checked out. In the end the final hurdle was the connection from the coils to the spark plugs. I had them flipped, though I'm not sure how that happened.

Glad to hear you got it resolved. Now if you've got better weather than we've been having (miserably hot and humid), get out there on that lake and enjoy. :lol: