ignition switch testing

How do I test the keyed switch on a gas TO35 ? Thanks

Welcome florizark!

Could you give us a little more information please.

Is the switch still on the tractor or off?

What kind of problem are you having?

You will need to have a test light and/or a multimeter to do the tests.

Well as with any switch if you have a VOM you test it by setting the meter on ohms and then hook the lead to the switch with the wire off of it and flip it on and you should get zero ohm and when off you should read an open.

Now if your having trouble with say one time you turn it on and your tractor will start then the next time it will not that could be the switch of a loose wire or other such thing.

Since I don't know your exact problem or exact switch or if the tractor got modified over the years I cant provide any specific answer but can provide a few basic guidelines.

LETS TALK ABOUT A GENERIC IGN SWITCH (may or may not be on your tractor no warranty) FEEDING AN IGNITION COIL WHEN ON

(A) BASIC SHORT SIMPLE CHECKS

As far as its IGN OUTPUT terminal assuming it feeds an ignition coil??? that should read "near" (may be some I x R voltage drop if current flows) battery voltage (12.6 if a 12 volt and charged or 6.3 if a 6 volt and charged) with respect to ground when its ON, but no voltage when OFF WELL DUH . Likewise with the ignition switch ON it should send hot battery voltage down to the coil if the switch is good and all the wiring etc.

With all the voltage sources removed or other possible current path providers, if you had an ohmmeter across the BAT INPUT and IGN OUTPUT terminal it should read an open circuit (near infinity ohms) when OFF but near zero ohms when ON.

It can happen the switching contacts (like between BAT input to IGN output) get burned or loose or resistive in which case instead of zero ohms when ON it may read like a few ohms (0r open infinity if a total failure) and you would have a voltage drop when feeding a coil and that can weaken the spark.


(B) MORE DETAILS


START FUNCTION in the event you had a type of switch (may or may not have such) that in addition to feeding the coil served to start the tractor its similar in that in the START position it would send hot battery voltage to a starter solenoid (if your tractor has that arrangement) so you need to test for voltage when in START similar to the above to insure the contacts are good and closing and non resistive. You may instead have a push start button, I have no idea how your tractor may have been modified over the years, just trying to cover bases so don't have a calf if your tractor is different

If an ignition switch is good and your battery is full charged there should be "near" (may be I x R voltage drop if current is flowing) 12.6 volts (6.3 if a 6 volt battery) on its BAT/INPUT, same as the battery voltage unless resistance is present and current is flowing, and then on the IGN OUTPUT when the switch is ON there should again be close to that same charged battery voltage which is 12.6 (6.3 if a 6 volt battery) BUT MAY BE LESS IF THERE ARE RESISTIVE CONTACTS AND CURRENT IS FLOWING CAUSING AN I X R VOLTAGE DROP. When an ignition switch is on and the points are closed and the coil is conducting current if the coils input voltage (unless a ballast) is very much LESS then the full charged battery voltage of 12.6 (6.3 if a 6 volt battery), YOU HAVE A BAD RESISTIVE SWITCH OR BAD RESISITIVE WIRING OR A BAD CONNECTION.

Best I can offer not knowing your switch or problem or mods over the years

John T BSEE, JD Long retired Electrical Engineer so no warranty, hope this helps, post back findings or other info or questions

Best wishes, God Bless, and Happy New Year to you and all here

Original TO35 owned since new. Original key switch finally stopped working earlier this year. Replaced with OEM switch and starter button. Both rewired to original. After several successful uses, a fire started along a wire, and burned lead from ammeter gage to regulator, and from regulator to alt. Fire out tractor started and ran several more times, then would not start. I can jumper the motor to turn over but no spark from coil and won't turn over through the switch. I found one wire from ammeter to regulator frayed & grounding out, probably started the fire. 12 volt neg. ground. I can't get back to it for a couple days or perhaps week. I planned on testing from switch back through regulator, starter button, etc. to eliminate cause without just replacing lots of parts. Burned wires replaced and battery charged at max charge. Come to think about it perhaps the neutral safety switch has been compromised, perhaps I could bypass that and try again. Thanks, Happy New Year!

Since there is no spark or start from the switch, sounds like there is no voltage going to the switch.

Does this have an alternator? If so, is it an externally regulated alternator? If that is the case, and a wire burned from the regulator to the alternator, something is wrong in the alt/regulator, and that will need to be addressed to get it charging again. Typically, when converting to an alternator, an internally regulated alternator is used and the old regulator is no longer in circuit.

Same thing, if you meant to say generator. Any wire that burned all the way from the amp meter to the generator, something is seriously wrong and needs to be checked before it does it again. For this to happen, both the contacts in the regulator would have to be welded AND a short to ground inside the generator.

Back to the ignition switch... Check the "BAT" terminal on the back of the switch, see if there is voltage there.

If no, the switch is probably good, just no voltage getting to the switch. Check the amp meter, it may have burned open internally when the wire shorted.

It there is voltage to the switch, turn the switch on, check the "IGN" and "BAT" terminals, should be voltage there. Turn to "START" should be voltage at "IGN", "START", and "BAT". If it has a separate start button switch, check it the same way, should have voltage to the switch, and coming from the switch when held in.

Be very careful when working under the dash or with any electrical problem. I like to loosen a battery cable so it can be quickly removed should something short out. And be absolutely sure it is in neutral! Anything can happen, could crank or start when you least expect it!

Okay, recently got back to the original project and question. The New key switch and the OLD starter button both test well and should work. The volt regulator did not show any response from my inexpensive VOM but when I opened it up looked like it took an direct hit from lightning, so that part is to be replaced. I think I will forgo the alternator for the time being and just work off a charged battery to get back to work with the tractor. I believe it should run without the alternator, as over the years I have run numerous tractors and pump motors without one, but would like someone to weigh in on that. Money is a concern and if I can get by for a while that would help. Thanks.