Ask the Mechanic

Backward Switch

On Off Switch (Steve Thompson)

READER: I am restoring a John Deere A tractor that is equipped with a magneto. I finally got fire out of the magneto, but I'm not sure how to shut down the tractor. Every switch I find works backwards. When the magneto is grounded to kill the tractor, the switch shows on. A push and pull switch is backwards. I have to pull it out to kill the tractor and push it in to run the tractor -- backwards -- same with a key switch. I asked around the coffee shop, and one senior farmer told me that with a magneto, simply set the idle so low that you can kill the tractor with the throttle. Another "Poppin' Johnny" guy said it is recommended to just shut off the gas in order to kill the tractor because it likes to flood anyway.

STEVE: The magneto needs no voltage to it. All normal switches are designed for distributor systems, which require voltage. What I personally do is buy a switch with an on and off label, and turn the label upside down -- problem solved. On is kill and off is run.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


Past Issues