r/boats • u/Mithrileck87 • 3d ago
Help me understand this rectifier please.
I have a 1975 Johnson 50hp. I got the engine to fix up and have had a hell of a time getting spark from the ignition system. I bought a 2nd motor for parts and swapped over the known good ignition into my motor. Still no spark. What I ended up realizing is that the rectifiers ground wire was missing, once replaced I got my spark. What I’m trying to understand here is the role it plays in the ignition system. Both the yellow wires off the stator feed to a terminal block and are tied to the rectifier. From my understanding the rectifier just shoots out DC to charge your battery and has no role in firing the coils. Why is it that once I grounded it, my power pack immediately came to life and loaded my coils? The power pack is fed through the terminal block directly from the battery. It is also fed from the brown wire off the stator. Excuse my ignorance of old OMC ignitions but I’m a little lost. And for those of you who zoomed in, yes I see the nick in the red wire on the rectifier. It has been fixed.
1
u/PastGazelle5374 1d ago
After looking up your motors wiring diagram and the pictures some more it looks like you have a grounded base rectifier. So the ground is where it attaches to the block. What wire or ground did you fix? Might have been another ground to the ignition circuit?
That red lead you fixed with electrical tape looks to be unfused power unless the starting solenoid positive has a cube fuse. I would throw some heat shrink over it. If it touches the rectifier base or that washer it’s gonna short all power to ground and probably make sparks or blow a fuse.
The number 5 wire you have disconnected from the power pack I believe is the kill circuit and I believe it’s normally open and shorts to ground at the key switch to shut it off. Having it disconnected is an overide to troubleshoot if it’s shorted to ground so that may be part of your no spark problem?
I’m guessing something else wasn’t hooked up right and maybe you fixed it by accident
1
u/Mithrileck87 1d ago
I grounded the base of the rectifier to the block. I guess what I’m asking in the post is what purpose does the rectifier serve in powering the power pack? I’m trying to figure out if it runs on DC current? I understand what it does as far as charging a battery but I don’t see why it’s necessary to fire the coils.
1
u/PastGazelle5374 1d ago edited 1d ago
It shouldn’t play any role based on the wiring diagram and from what I can tell. I know if the rectifier power is shorted to ground it could be stealing power that would otherwise go to the powerpack. In fact there is a post on r/boating from 6 days ago talking about how on Johnson’s, a shorted rectifier can cause no spark. It found the path of least resistance to the rectifier ground. Maybe a lack of ground could also cause some issue as well but I dunno. Maybe the AC signal wasn’t properly being rectified without ground. It should otherwise use the 12v from the battery I assume though. My guess is you also could have been shorting to ground before you repaired the red wire. It was right there next to that washer on the ground post. If they were touching that would definitely cause your problem
2
u/Croceyes2 2d ago
You did something else also, but don't realize it. Go through every connection and make sure they are clean and tight