My Tractor Forum banner

horse tiller

2141 Views 18 Replies 5 Participants Last post by  utfyrfytr
I have an approximately 20 yr old Horse Troy Bilt tiller with the B&S 10hp electric start engine. Four or five years ago I went to start it and the battery was dead so I jumped it with my automotive battery charger (you can see where this is going) and all of a sudden I had smoke pouring out from under the flywheel housing. I turned the engine over using the pull starter and had no spark. I pulled the housing and found the ignition coil was fried. I installed a new one and the motor started and ran fine using the pull start. This spring I decided I was tired of pulling the rope so I installed the battery from my riding lawn mower along with a new switch turned it over and immediately fried the ignition coil again.
Question is why am I frying the coil when it has no voltage going to it other than what is being supplied by the coil as it is running. The only thing that I have come up with is there is voltage being generated by the charging rectifier and maybe I shorted it out. When I removed the rectifier I did not see any obvious indication of a problem. Is there a way to test the rectifier or can I have a direct short that is causing my problem? Any help is appreciated before I cook more pieces of this thing.
1 - 19 of 19 Posts
Battery is in backwards, shorts in the wires?? Roger
Checked those things, the battery is correct and nothing obvious with the wiring. The only thing I can think to do is remove each wire and by process of elimination try to figure out what is wrong. Wouldn't you think that if it fried the coil there would have to be a direct short to the motor? If the stator is bad how would it carry enough amperage to cook the coil and still not even discolor the wire that goes up to charge the battery? Sorry about the rambling I'm just thinking as I type. Thanks for the thoughts and if you come up with any other ideas please let me know. Terry
Normally no battery voltage goes to the magneto coil. I would check the kill wire going to the magneto and see if it's melted into another wire causing a cross short. Might even be inside the ignition switch, rust or broken inside. Unplug the kill wire from the magneto and test with a voltmeter.

When you first fried the stator (produced smoke) you probably connected the battery jumper leads backwards and the stator diode was forward biased resulting in a high current through the stator windings, similar to connecting the jumper leads to a vec battery backwards and frying the alternator diodes and alternator. :tango_face_sad::tango_face_surprise
I'm leaning toward thinking the stator is the problem. Is there a way to test it without the engine running? Can I use my ohm meter and check to see if it is grounding to the motor and causing a short?
The kill wire did show sign that it had over heated but it was not shorted to any other wires. The ignition switch is new. Thanks for your input, keep the thoughts and ideas coming.
Key switch is bad and backfeeding 12 volts into the coil and frying it.....swap out the switch along with a new coil.........
The switch is new and I'm not saying it couldn't happen but, I don't see how it could back feed into the magneto type coil when there is no 12 volt lead going to the coil to start with. Where is the voltage coming from that goes from the switch to the coil? Is it going to ground and making the entire tiller one large short? Again I'm not saying it isn't possible because if I knew as much as the rest of you I wouldn't have to be asking silly questions. I would be the one helping to supply answers like you are. Thanks for your input.
The switch is new and I'm not saying it couldn't happen but, I don't see how it could back feed into the magneto type coil when there is no 12 volt lead going to the coil to start with. Where is the voltage coming from that goes from the switch to the coil? Is it going to ground and making the entire tiller one large short? Again I'm not saying it isn't possible because if I knew as much as the rest of you I wouldn't have to be asking silly questions. I would be the one helping to supply answers like you are. Thanks for your input.
Cranman is correct:

If the key switch is for electric crank is the spring loaded start position type, it has 12v on the B terminal sends 12v to the starter solenoid (S) terminal to en-gauge the starter and in your case is also sending 12-volts to the magneto kill wire sometimes. (may or may not be a direct short internally in the switch, just intermittent.

To test, disconnect the kill wire at the magneto coil, connect a voltmeter to the kill wire or a 12v light bulb and use a battery or battery charger and in all positions of the ignition switch their should NOT be any voltage at all to the kill wire. (use a 10 amp in-line fuse to prevent more smoke in case of additional shorts due to melted wires) When the switch is off the kill wire to the magneto simply is grounded through the ignition switch, You switch is probably bad internally or someone has installed the wrong switch or Bubba has done some hack wiring and got er wired wrong.

Just because the wiring harness connector plugs onto those tiller and lawn tractor switchs does not mean that you have the correct switch for your wiring harness. (several different versions of the switches electrically internally):tango_face_surprise
Went out and ran the test on the switch and it shows 12 volts to the kill wire when in the run position. What upsets me is it is a new switch. I specifically replaced the original switch in case it was what caused my original problem. I have owned this tiller since it was new and I knew there had not been any funky wiring or Bubba's working on it, except me.
Cranman thanks for your help. I didn't see how the switch could get 12 volts to the coil and thought you might be thinking of a 12 volt coil like in the old cars. When Forest explained how the problem could occur and the test procedure then it made sense. Thanks again.
Forest, thanks for walking me through the test procedure and your explanation of the problem. I'll order a OEM switch tonight.
You might want to post a question over in the tiller section of this forum about correct part number for the switch using a MODEL NUMBER from your tiller. and lots of info in the tiller section here about locating model numbers,Service manuazls, etc. their is also a guy that you can contact by the name of chzuck on this site (if someone don't chime in first) that knows Gardenway, MTD-Horse tillers inside and out and he can PROBABLY TELL YOU EXACTLY WHAT YOU NEED. Here is a direct link to the tiller section. Post up your model number here and maybe someone can help you get the correct part number for the switch. The OEM may not even be available and you might have to hack and re-wire.

Good chance their is more than one style make of switch switch over the years and the parts place is selling you the wrong one for your wiring harness. (and I think maybe MTD is now the supplier of parts for the Horse Tray bilt and MTD part numbers are not always right on correct. Last resort, get a electrical tech to help you rewire for the new switch if it also shows voltage being supplied to the kill wire.

You probably do not have the old OEM switch. If you did you look at the location of the S, B, M terminals on the rear as a comparison. Also if the terminal codes on the replacement switch tabs on the rear is in same location as your existing switch you will have the same issue with the new switch.
Forest, thanks for the information. I thought I was posting in the tiller forum, if I'm not where the heck am I? LOL

I have owned this tiller since it was new, I have the original owners manual and that is where I found the part# for the key switch and I do have the original switch and made sure the pins were the same and in the same S, B, M locations. Maybe I just received a bad switch.

When looking up a new switch last night I found that Tractor Supply carries the MTD OEM switch and they have a store about 5 miles from my house so I will be paying them a visit today. They are suppose to have the switch in stock at that store.

You can be sure I will test the new switch before I install it and will be testing everything one piece at a time as I put this thing back together.

Thanks again for all of your help and time that you have spent on this.

I would also check for voltage on the kill wire with the wiring harness unplugged from the ign switch. If you still have voltage some wires are melted together inside your wiring harness. (due to when the OEM switch first shorted out)

AND my fault you are in the Tiller forum.
Well I checked the kill wire and no voltage, hooked up the new switch did the no voltage to any terminal test and once again I have power on the kill switch terminal. In analyzing the poles on the switch there is B, S, L, M and G. The L is probably for lights and would have to be hot in the run position to be able to have lights when working. The original switch is the same. We have to be missing something here. I think I will PM Chzuck like you said, ask him to read the thread we have going and see what he has to say, because I am at a loss. I don't know why the kill wire would be on a hot terminal. Something else I just noticed while looking through the owners manual is in a stock picture talking about the electric start the plug going to the ignition switch only had 3 leads coming off the switch while mine has 4. The 3 makes sense the 4 doesn't at least not to me.
B=Battery positive( usually red wire)
S=Start to solenoid (applys 12v to solenoid during crank)
G=Ground (negative to chassis ground) usually green
M= (Usually black)kill wire to magneto. Applies ground to magneto wire when key is off. NO OTHER CONNECTIONS inside the ignition switch when in other positions.

You say you still have the old OEM switch for when the tiller was new and all worked ok?

If so look closely at your OEM switch and the new replacement switch and see if the letters G, M, S, etc are in the EXACT same locations on the back of the switch.
Summary: Your wiring harness plug that is going onto the replacement switch has the M wire connected to the wrong terminal.

What you could do (so as to use electric start without burning out magnetos) if you don't want to trace and re-splice your existing wiring is leave the kill wire disconnected from the ign switch and install a Normally Open push to kill switch to the magneto wire or just choke the engine for kill. Don't be surprised if the new ignition switch might not crank the starter and require finding the S start wire and sending it to the solenoid for crank.

I would guess that maybe Gateway/MTD (MTD is know for such also) had a slight change in electrical wiring and parts going by a serial number break over, your owners manual for example maybe being for maybe a slight later model and your tiller itself slightly older and therefore your parts manual does not exactly match your Gateway tiller. Their were several minor changes to those going units mechanically. (and apparently electrically also. Shame that you had to discover such the hard way, burning out coils.
If have a voltmeter and ohmmeter WE can probably get you to connect your wires to the right places.

When OFF the M (coil kill wire ) terminal is connected to G. When the key is in any other position such as run start, etc, the M terminal and the coil kill wire is open to all other terminals.

When key is switched to on the M terminal is ungrounded and the B terminal MIGHT make to the Light terminal. (some switches have a extra position just for the lights only which is first on position.

When turned to the spring loaded crank, the B terminal to the Start terminal which applies 12V positive goes towards the starter solenoid little terminal.

Normally for 4 wires Red =B, Black = M coil kill, Start (can be any color sometimes white, and Green to G=ground.

Your coil kill wire is being connected to the wrong terminal of your ign switch.. If the coil kill wire only has 12v when key is in start it is connected to the S terminal instead of the M terminal of the switch.

What are your wire colors?
What is the exact Model number and name, like Gateway, MTD, or ???? (maybe we can find a 4 wire wiring diagram) if we had a name and model from your units tag on the chassis, not the model number from your owners manual.
PM chzuck is a good idea, send him the exact numbers off your machine chassis. I think he even has a tiller service and maybe a website. listed at his public profile. He has helped me get through the mechanical of the old Horse tillers and finding Service manuals online.

Do you have a voltmeter and ohmmeter?
I do not have a tiller service, but do work on them for friends and others. I have a friend who was service manager at GW in the early 80's. I have a 1982 Horse with electric start, which I removed. The switch on it only has 3 wires and none go to the ignition coil. The ignition coil gets grounded via the wire on the throttle assembly on the engine. We need the s/n that is stamped on the top right side of the wheel drive gearbox.


Here are some photos of my setup.


Thanks to all for the information. I have given up and just removed the kill wire that had voltage on it in the run position. There is obviously a problem some where and maybe sometime in the future I will find it but for now the tiller is running with the electric start and not burning up coils. I can't kill the motor at the key switch but my model has a second shut off (just an off on turn to ground switch) on the blower housing. The kill switches in the handle bars that kills the motor if it is in drive also still work so I'm pretty happy about where I'm at. Wish I knew what is wrong but maybe in another life. For here and now nothing is perfect.

I appreciate the time thought and effort that each of you have given to this thread. Maybe sometime in the future I will be able to help others. Enjoy your weekend.

1 - 19 of 19 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.