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Magneto Kill Switch Wire Shorted to Ground

#1

Grousemansav

Grousemansav

Ok so my Craftsman lawn mower was working fine until this morning. It is a 2002 mower with a 6 ½ HP Briggs & Stratton Model123K02-02260E1 engine. I used my spark tester hooked up to the spark plug and there was no spark. So then I hooked the tester directly to the block and there was spark. I changed plugs but still the same results. So I’m thinking it must be a really weak spark. I cleaned the magneto and reset the flywheel gap to one business card thick. Still the same results.

Then I looked at the kill switch and everything looked OK. I unhooked the kill switch wire and put my VOM between the wire and the block and there was 0 ohms resistance which says to me that the kill switch wire is shorted to ground. I checked the condition of the wire back to the magneto and it is good.

As far as I can figure, that wire from the magneto should not be shorted to ground until the kill switch closes for safety. That being the case I figure it must be internally shorted in the magneto and I need to replace the magneto.

I am relatively new to this so would really appreciate any input from experienced repairman.

Stay safe, Grouseman


#2

R

Rivets

If you believe everything you see on the internet then you can follow that guy’s procedure and replace the coil. I don’t believe half of what I see, but I have been wrong before. I have not found a reliable way to test today’s coils which contain a Hall effect module in them. I suspect you have a short in the wire between the coil and the kill switch which is located by the flywheel brake. Before I would spend money on a new coil I would triple check this kill wire. Just my opinion, as you can see by my signature isn’t worth much.


#3

Grousemansav

Grousemansav

Rivets said:
If you believe everything you see on the internet then you can follow that guy’s procedure and replace the coil. I don’t believe half of what I see, but I have been wrong before. I have not found a reliable way to test today’s coils which contain a Hall effect module in them. I suspect you have a short in the wire between the coil and the kill switch which is located by the flywheel brake. Before I would spend money on a new coil I would triple check this kill wire. Just my opinion, as you can see by my signature isn’t worth much.
Click to expand...
I checked the kill switch itself thoroughly and it is functioning properly. The insulating sandwich where the wire attaches is working fine.

Grouseman


#4

StarTech

StarTech

To determine if it is coil or the kill circuit disconnect the kill circuit at the coil's kill terminal and test.


#5

B

bertsmobile1

remove the kill wire at the magneto
Put your spark tester on the plug and lay the plug on the block
Spin the flywheel and see if you have a spark


#6

Grousemansav

Grousemansav

OK so now the plot thickens and I am totally confused. Yesterday I disconnected the kill switch wire and put everything back together. Low and behold it started right up. I had to pull the plug wire to stop it. This is really baffling!! Now I'm thinking it's got to be the kill switch but why is the kill switch wire shorted to ground at the magneto? Help!!!

Grouseman


#7

R

Rivets

The kill switch wire on the coil (the one you removed) goes from the coil to the kill switch which is located by the flywheel brake assembly and shorts to ground when you release the bail handle . By removing the wire you disabled the kill switch. If the wire is bad or shorted to ground, it will acted like a kill switch and the engine will not run.


#8

G

Grounded

Grousemansav said:
Ok so my Craftsman lawn mower was working fine until this morning. It is a 2002 mower with a 6 ½ HP Briggs & Stratton Model123K02-02260E1 engine. I used my spark tester hooked up to the spark plug and there was no spark. So then I hooked the tester directly to the block and there was spark. I changed plugs but still the same results. So I’m thinking it must be a really weak spark. I cleaned the magneto and reset the flywheel gap to one business card thick. Still the same results.

Then I looked at the kill switch and everything looked OK. I unhooked the kill switch wire and put my VOM between the wire and the block and there was 0 ohms resistance which says to me that the kill switch wire is shorted to ground. I checked the condition of the wire back to the magneto and it is good.

As far as I can figure, that wire from the magneto should not be shorted to ground until the kill switch closes for safety. That being the case I figure it must be internally shorted in the magneto and I need to replace the magneto.

I am relatively new to this so would really appreciate any input from experienced repairman.

Stay safe, Grouseman
Click to expand...
Grouseman, did you ever figure this one out? The only difference between your case and mine, is that my mower starts up despite having continuity between kill switch-magneto ground wire and exposed metal on engine when the bail handle is pulled and the kill switch is open. Even though my mower works, I can't figure out why. It seems like it should be grounded with no spark, but lo and behold, it runs fine.


#9

StarTech

StarTech

Come on you will have a continuity beep when measuring as you are measuring across the coil's primary winding which has a resistance of about 1.5 ohms. There no way for a DIYer to test these electronic controlled coils. You test in this case for open circuit of the kill tab which is normally directly attached to the ungrounded side of the coil.

In order to test other plug and play method requires a very expensive coil tester which most shop do not have either due it high costs.


#10

G

Grounded

StarTech said:
Come on you will have a continuity beep when measuring as you are measuring across the coil's primary winding which has a resistance of about 1.5 ohms. There no way for a DIYer to test these electronic controlled coils. You test in this case for open circuit of the kill tab which is normally directly attached to the ungrounded side of the coil.

In order to test other plug and play method requires a very expensive coil tester which most shop do not have either due it high costs.
Click to expand...
Not sure I follow. I was testing for continuity between the kill wire and the block when the circuit is open (kill switch open, bail handle pulled back). When kill wire is connected to magneto, I have continuity, when not connected to magneto, I don't. So you say there is continuity across primary winding, which makes sense. The current needs to reach spark plug. But should there be continuity between the kill wire and ground when the circuit is open?

As far as I understand, that would mean the magneto circuit is grounded when the kill switch is open, which would provide a direct path for current to ground instead of across spark plug gap, which would mean no spark.


#11

B

bertsmobile1

The kill wire is a GROUND wire
Ground = off
open = on
A spark when the wire is connected to the block with no plug but no spark with a plug = weak magneto or bad connection between plug cap & HT wire


#12

StarTech

StarTech

And don't forget a bad plug. Even plugs the shows spark outside the compression zone can be failing under compression load.


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