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minniemo705

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My first magneto- Fairbanks morse on a U. Does the power wire that would go to the coil hook on the mag on the small terminal below where the plug wires hook on?
 
Ok, so did some reading and you don't power it which would explain why the one terminal on the on/off switch is grounded. My tractor is a 46 that had rotten wires. I could really use a wiring diagram if someone has one because now I'm trying to figure out where the wire coming off the on/off switch goes. On the tractor with distributor it would go to coil, on mine it is busted and hanging close by mag which is why I thought it went there. None of my U books have a diagram plus they are all for the later tractors with the split block. Thanks
 
You NEVER EVER EVER EVER connect a power wire to a magneto or you will destroy it's (internal) coil.

Magnetos make their own power, and the little terminal can be GROUNDED (at the mag or wired to a remote grounding "kill" switch) to "kill" the spark to stop the engine, but NEVER EVER EVER EVER connect power to it!


On the other hand, there are tractors out there running with magnetos that have had their internal coil removed, and an external coil wired in to make them operate just like a distributor.
 
on a magneto there is usually a ground wire running to a terminal on the mag. which grounds it to shut the engine down. no power wires running to magneto.
 
Ok. I didn't put power to it. I watched a video and found that out. But you've just explained where that wire from the on/off switch goes. I knew it had to kill it somehow, so that would be that small terminal on the bottom of the cap. Next question- It is only sparking sporadically. I put a new condenser in it and the points are good. turning it on tractor and off and by hand no difference- very inconsistent spark. (However that spark does make you jump if your touching that rotor and turning it by hand.) It does click nice and loud. So is it's coil bad?
 
OK. I didn't put power to it. Watched a video and figured that out. But that does explain where that wire from the on/off switch goes. I knew it had to kill it somehow, so that would be what that terminal on the bottom off the cap is for. Next question. The spark is extremely inconsistent. turned it on tractor and off the tractor by hand- no difference. the points are good and I put a new condenser in it. So is it's coil bad?
 
I have the proper testers for the coil & condenser. If the points are good & clean, the new condenser could be bad too. Or the coil or the magnet is weak. I have the magnet charger too. Without the tools, you are just guessing. Let me know. Thanks.
 
(quoted from post at 16:20:28 10/14/19) OK. I didn't put power to it. Watched a video and figured that out. But that does explain where that wire from the on/off switch goes. I knew it had to kill it somehow, so that would be what that terminal on the bottom off the cap is for. Next question. The spark is extremely inconsistent. turned it on tractor and off the tractor by hand- no difference. the points are good and I put a new condenser in it. So is it's coil bad?
Click to expand...

"The spark is extremely inconsistent"

The MOST likely cause of that is dirty or sticking breaker points. USUALLY, a bad coil or condenser will give a no spark or a consistently weak spark,spark that comes and goes is USUALLY linked to the points.

If they are not badly pitted, you can burnish them by drawing a clean strip of white cardstock through them repeatedly until they are shiny, then, with the points "open" clean them with spray electrical contact cleaner and allow to air-dry completely before again checking for spark.
 
Some replacement magneto's were battery powered. Had a Wico on a U which required battery voltage. It was basically a distributor in mag housing. Terminal on mag is for kill switch which grounds coil. First U's had knife switch on steering column. Later U's had switch on dash. Magneto that U's came with were FM4bk4.
 
Disconnect wires/condenser at points. Use a continuity meter to check points when closed. This will help determining whether or not points are clean. I have had to file new points to get a good circuit.
 
I am guessing. I can't get the points any cleaner, and the condenser is fine on my other U's. Are the condensers for a mag and distributor different? The coil has corrosion where that spring is in, and that armature looks filthy bad. I am not to interested in rebuilding a mag. I'd rather spend some extra and buy a new one that has been tested and is ready to go cause I have way to many projects to get to and this one is stopped at something simple. Anyone got a good working mag for sale?
 

If your on/off switch is not original to the tractor--i.e. a newer one--keep in mind that it is probably designed for a distributor ignition and will work opposite of what you might expect--in other words, it needs to be in the off position for the tractor to run. Turning it on completes the circuit and grounds the mag.
I've seen several tractors with push/pull type switches where you push it in to run the tractor and pull it out to stop it.
Just something to be aware of.
 
I will have to check my stash . If I don't have one I can redo yours for a small fee. My mail is open on classic. Please let me know. Thanks.
 
Have done all my own for many years. Seldom any parts required. Would love to have a charger and test bench . Have coil and cap checker. Been doing electronics for 43 years.
 
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