How's An Ignition Switch Work?

MikePA · Jun 17, 2004

How\'s An Ignition Switch Work?

Specifically, in the Off position, no really. /forums/images/graemlins/smile.gif My Wheel Horse garden tractor wont shut off when the ignition switch is turned to the Off position. I have to pull the choke out to kill the engine. I've replaced the original ignition switch (20 years old!) and it still won't shut off. I have the wiring diagran and I am 'electrically challenged' and can't figure out how it's supposed to work, so I can't troubleshoot it.

RobS · Jun 17, 2004

Re: How\'s An Ignition Switch Work?

I'm kind of guessing here Mike, and I didn't even sleep in a Holiday Inn Express last night /forums/images/graemlins/confused.gif

Somehow the off position on such a simple system should ground the juice to the coil or eliminate the voltage to the coil. This will eliminate the spark which will obviously kill the engine. Without the grounded coil feed the engine continues to run. I'd say you've got some corroded/worn contacts in the switch itself.

Again, I'm hardly speaking from authority here /forums/images/graemlins/smile.gif

Junkman · Jun 17, 2004

Re: How\'s An Ignition Switch Work?

Without the wiring schematic, I can't say for certain. Most small engine ignition switches have a terminal that grounds out the magneto when you switch them off. If it has an electrical starter that is battery operated, the ignition switch make a connection through the starter solenoid to the batter to provide power to the starter to start the cranking. Once the engine starts, the spinning flywheel throws the Bendix drive (the gear that engages the flywheel that is mounted on the starter armature shaft) and then you let go of the key and it springs back to the "run" position. If there are points on the engine, then the starter switch breaks the connection to the positive side of the ignition coil. Since you have already replace the ignition switch, I would be looking for a broken wire. Almost all small engine ignition switches have the same terminal configuration on the rear, however the internal connections are all different and even if it looks the same, it in all probability isn't internally. Hope that this helps you better understand how it works.

Lazy · Jun 17, 2004

Re: How\'s An Ignition Switch Work?

Hi
What is the model number? I have a service manual that covers several wheel horse yard & garden tractors. maybe you could post the wiring diagram you have. When was the last time it worked?

Charlie.

Soundguy · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

That switch in the off position either grounds the maggy output.. or opens the mag ground reference.. but I'll bet on the grounding the maggy.

Also.. choke to kill an engine will do just that... kill it over time. Choking to kill an engine causes fuel dilution of the oil.. washes the rings down and reduced lubrication on the cylinder walls for the last few revs... probably the only worse way to kill it would be to pour sand or water down the air intake /forums/images/graemlins/shocked.gif /forums/images/graemlins/crazy.gif

I workeed on lots antique engine where people thought the choke was the kill cable... oil turns to 0w0 pretty quickly...

Get a jumper wire to test out your faulty ignition switch.. ground the incoming wire that hits that position.. if it kills it.. there's your answer.. also.. the kill wire could be broke down near the maggy..

Soundguy

MikePA · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

Attached is a schematic of the switch in the OFF position.

RobS: I'd say you've got some corroded/worn contacts in the switch itself.
Already replaced the switch. /forums/images/graemlins/grin.gif

Junkman: Hope that this helps you better understand how it works.
It does, thanks! The tractor, a Wheel Horse GT1600, has a magneto and no points.

Lazy: When was the last time it worked?
About 2 weeks ago.

Soundguy:Also.. choke to kill an engine will do just that... kill it over time.
I kinda thought this and told my wife the same when she said it was 'cute' that the little tractor didn't want to shut off, i.e., it wanted to keep on working. Come to think of it, this started happening when she decided to start cutting the grass again.

Where would I start looking for a broken wire, at the engine near the starter?

_RaT_ · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

Check your ground with an ohm meter at either G, M or A on the switch. When at the off position all three will be grounded. With a clip on ground and one on G,M, or A you should read a short or nearly 0 ohms. The case of the switch must be grounded to either the frame or a terminal provided to allow you to ground the switch in the event it is mounted in a plastic or other non conductive surface. What make is the engine? I have a Kohler that simply has a black wire along with other wires that connect in via a connector similar to what would be found on a trailer with 4 conductors in a flat connector. Good luck. Electrical problems can be a pain especially when they are intermittent.

MikePA · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

 What make is the engine? 
B & S IC Twin

BB_TX · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

Mike - Everyone is right on with the grounding of the magneto. Looking at the schematic, when the switch is in the off position, the switch wire to the magneto is supposed to be grounded thru the switch. Also, you will note that if the PTO is engaged and the seat switch is made (seat unoccupied) it will also ground the mag to kill the engine. Does that work?
Check the magneto wire (the blue wire) thru all the locations shown on the schematic. Also there should be a ground wire to the switch. The diagram does not show what color that wire is. Find that wire and check it.

MikePA · Jun 18, 2004

Re: How\'s An Ignition Switch Work?

 Also, you will note that if the PTO is engaged and the seat switch is made (seat unoccupied) it will also ground the mag to kill the engine. Does that work? 
That 'safety feature' has been bypassed for several years. /forums/images/graemlins/tongue.gif

 Also there should be a ground wire to the switch. 
I 'think' this (grounding the switch) is working because when I tried to start the tractor when the switch was not mounted in the 'dash', nothing happened.