# Ever "Smoke Test" an Ignition Switch?



## Bob Driver (Nov 1, 2017)

Ignition switches can be a real PITA to figure out sometimes. Just because an ignition switch has 5 terminals, doesn’t mean they are interchangeable by using the OEM plug connector. It all depends on how the internal contacts are positioned as to what function they control and how your machine is wired. I’ve seen at least 10 variations to the way a simple 5-prong ignition switch can function. Add to the confusion by making it a 3-position(off, On, start), or 4-position(off, On1, On2, start). There is somewhat of a code that is used to describe the terminal functions, but the only way to really figure out how your switch works is by using a VOM and testing each terminal as to function. Some ignition switches will have the terminal coding marked, but you can’t count on it. Here is the most common coding used on mower ignition switches that I’ve come across:

*B -- BATTERY*… Brings 12VDC power from the battery into the switch. Usually has a 15-20A fuse in-line

*S -- START *….. Sends 12VDC to the starter relay when the key is in the spring-loaded start position

*M -- Magneto* … Connects to magneto(s) and is used as the “Kill” circuit by connecting the magneto(s) to ground

*L -- Load* …. Supplies 12VDC power to the terminal with the key in an On position

*G -- Ground*….. Ties switch into ground circuit of wiring harness

*Y -- Charging* …. Supplies charging voltage to the B terminal (Battery) when the key is in an ON position. Usually comes from the Rectifier/Voltage Regulator

*A -- Accessory*…. Supplies regulated 12VDC power source with the key in an ON position

*I -- Ignition*…. This can be the most confusing of all. Sometimes used to carry 12VDC to the points with the key in an ON position, but I’ve also seen it provide the same “kill” function as the M terminal

*R -- Regulator/Rectifier*… 12VDC power. Sometimes used to bring power into the switch (Like a Y terminal), or can be used to provide 12VDC out of the switch. Connects to B terminal with the key in an ON position

*X -- ????*.... Never had the joy of trying to figure that one out

Here’s a chart showing several variations as to the way mower ignition switches can be configured. The Red numbers in each diagram are the *Oregon part #* for that configuration of switch. I warned you they can be confusing, I’m just trying to help you avoid that “smoke test”. You know… Where you turn the key on that brand new ignition switch and the wiring starts to smoke??










This chart has been added in a larger, easier to read, PDF format to the Manuals section of this forum under "Ignition Switch Configurations"


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## Hoodoo Valley (Nov 14, 2006)

Very informative Bob. Thank you for sharing!


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## bontai Joe (Sep 16, 2003)

I've "smoke tested" some stuff over the years. I found out that once you let the smoke out, you can't put it back in. I know because I've tried.


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## Hoodoo Valley (Nov 14, 2006)

I had a smoke and fire episode once. 1947 Chevrolet truck. Cloth wire all nice and toxic!


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## Bob Driver (Nov 1, 2017)

If you end up with a switch that doesn't exactly match the functions on the female connector of your OEM wiring harness, you can use a "Terminal Removal Tool" to release the clips on the brass spade connectors and move them around to the position you need them. They run less than $10 on Amazon for a complete set


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## pogobill (Jan 31, 2012)

Time for me to jump in... Yes I have smoke tested an ignition switch...Yesterday. '48 Cockshutt 60. Turned over slowly.... the starter button heated up like an arc welder and the wire burnt off the back of the key switch.... I suppose that would count, huh? 
New switch on the bench, and new wiring in the works... need to pull the starter as well, I suppose.


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## Hoodoo Valley (Nov 14, 2006)

We've all been there Bill. It's going to be okay!


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## bontai Joe (Sep 16, 2003)

I smoke tested my right index finger once. That was the day I pretty much stopped fooling with electricity. It had bit me in the past, but that was the first time it cooked me. It's been about 34 years and the scar is pretty much gone now, but the memory is still fresh.


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