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74 T-16H (AC) ignition switch wiring help


Gilmer

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Hey again guys. My ignition switch broke on my Homelite T-16H, to the point where I can't turn the key to even test continuity of the switch and to compare it to the new switch I have. I bought a AM38227 (6 blade) ignition switch from a loca dealer because it's the only local switch that I can find that supposedly will work.  My problem is I'm not 100% sure if I know how to hook up what wires to which contact, so before I go guessing I figured I'd ask you smarter fellers. Thanks in advance. 

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20240418_213757.jpg

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I’m not very well versed on wiring as I usually just enlist my dad to do so. But I don’t think it should matter as long as everything that connected on the old switch just connects on the new one. As it’s all going to the switch to do practically things. I don’t think the specific posts matter, just my un-educated electrical assumption of course. Someone more versed will likely be of more assistance.

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PhanDad
1 hour ago, Gilmer said:

I bought a AM38227 (6 blade) ignition switch from a loca dealer because it's the only local switch that I can find that supposedly will work. 

First is the switch you bought for a magneto ignition rather than a "12v" ignition (think Kohler external coil).  You need a magneto ignition switch.  

Hopefully a pin-out diagram came with the switch so you can match up the wires (and maybe change the positions of the wires on the ignition harness connector). 

.  

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The key switch unfortunately did not come with any info, I bought it from a local John Deere dealer and the ignition type for this particular switch is for a magneto ignition. 

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Ronald Hribar

I think you have A Briggs 16 hp motor

so switch “should” be correct type.t

Doesn’t your wires just plug in the back of switch?

 

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PhanDad
11 hours ago, Gilmer said:

The key switch unfortunately did not come with any info

Then you'll have to determine the functions of each terminal with an ohm meter or other testing device.  Based on this pic of my T-12 dash (taken after I had started the hour meter install so the double yellow wire has already been disconnected):

IMG_5713.thumb.jpg.73da585204d96b625cba0c4115446b22.jpg

And this "wiring" diagram for AC Built Homelite tractors:

T16_WireOnlyColorCorrected.thumb.JPG.64769d018a9c0bef3b96462fc728a2fc.JPG

(Note the diagram has been corrected to match the wiring of my T-12 (diagram originally showed  light green (G in the key) wires for the "accessory" wiring).  

It appears the ignition switch has only 4 connections

dark green - 12V power feed from the circuit breaker (Battery)  

purple - the engine "start" to the solenoid after passing through the safety switches

yellow - 12V accessory feed

white - the magneto kill wire (I didn't color this wire)

I believe the original ignition switch is the same as this 3310H (Briggs magneto engine):

3310HIgnSwitch1a.JPG.c529db6f230bf7ee972e2ca3cb10484c.JPG

I think the functionality of the switch is:

"Off" - Ground (case) connected to the magneto "kill" terminal.  

"Start" - +12V terminal to the "start" terminal ("kill" terminal isn't grounded)

"Run" - +12V to accessory terminal

I don't think the accessory terminal is connected to +12V in the "Start" position. 

Your new switch probably has more connection options similar to this newer Simplicity 6 pin ignition switch: 

IgnitionSwitch1686734(was1716061)PinOut.jpg.2b25a045c0174054924f92dc3e81fbfe.jpg

Good luck with your detective work.  

And make sure you don't mistakenly feed +12V to your new magneto or it will fry.  

 

 

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SmilinSam

First off,  Bill ( @PhanDad ) has given you  great information. I'm goin to try and add something useful here too.

 

NEVER assume  tabs on a key switch are the same as a previous switch, or same as any other switch for that matter. If they are not labeled on the switch you NEED to  confirm what they all do with a multimeter. I set mine to  the audible" beep " when a connection is made. 

Since you know its a magneto ignition type switch, put the key in the off position.

Before I go any further, many modern John Deere type ignition switches are a 4 position switch instead of a 3 position switch. The extra position is for turning the headlights on. They do this instead of using a separate switch for the lights. They also generally have a tab that is grounded to the switch case or body. Most of the time you will see a metal band connecting the tab to the body. The meter will beep when you connect one wire to the tab and the other to the switch body.

Now, with the key off, find out which tab is grounded  only when the key is off ( other than a general ground tab which is grounded all the time) To do this, just touch one wire to the switch body and the other to the tabs till you find the right one. When you do, turn the key to the on position and the beep should stop. Turn the key off and it should beep again. This will be your  'M" or magneto tab. Note that the "M" tab will not be connected to any other tabs in the run or start positions

Next find the "S" or start tab. Turn the key to the start position and see what 2 tabs connect. One of those will be the "S" tab. The other will be the "B" or battery tab. Hint, usually the Start tab is  the one in the middle on top or above of the rest on a 5 or 6 tab switch. Not always though. Note that the "S" tab will not be connected to any other tabs in the off or run positions.

Those 2 were the easy ones. Now you need to find out what connections the other tabs have in relation to the different switch positions.

 

Hope this helps some.

 

Edited by SmilinSam
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Got it running this morning, I was concerned because I couldn't compare the old switches continuity because it was broken, so thanks so much for the help. Got to plow the rest of the garden from where I had to stop when it died. Now my next question is what is wrong with my tranny lever? I have to keep tension on it with my hand (pain) and it has a ton of play with it. I go faster in reverse than I do in forward and the spring lever doesn't seem to do anything at all but look cool. I don't know if I'm missing a piece or what. 

20240420_195544.jpg

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SmilinSam
18 minutes ago, Gilmer said:

 Now my next question is what is wrong with my tranny lever? I have to keep tension on it with my hand (pain) and it has a ton of play with it. I go faster in reverse than I do in forward and the spring lever doesn't seem to do anything at all but look cool. I don't know if I'm missing a piece or what. 

Sounds like the little ball that fits in the little hole fell out. This frequently falls out and gets lost if you ever take the lever assembly apart. The ball is what keeps the main control  lever in place when you let go of the spring lever.

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Definitely sounds like the problem, I don't recall ever seeing a ball there. Any idea on specs of it and pics? 

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SmilinSam
11 hours ago, Gilmer said:

Got it running this morning, I was concerned because I couldn't compare the old switches continuity because it was broken

Thats no problem really, as with the original switch you just figure out what tabs did what by running the wires connected to them. The main thing to keep in mind is not to run 12v to a ground tab or that M tab.

Wifes relative had a 9hp Landlord (no multi function keyswitch on that one) and rewired it putting the 12v battery wire to the wrong thing in the wiring system and fried at all. Literally had it on fire when he connected the ground to the battery.

 

As to specs or pictures of that ball on the control lever, I cant help. Havn't got any vickers  stuff around here right now.

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PhanDad
14 hours ago, Gilmer said:

I have to keep tension on it with my hand (pain)

 

2 hours ago, SmilinSam said:

As to specs or pictures of that ball on the control lever

Dad got the T-12 used - only 2 years young.  But this is how the hydro control lever came:

IMG_5389a.jpg.d70ced61958a604c07a58776e3961896.jpg

IMG_5390a.jpg.4f2abbd7b73f8e9285fde6360e3525d2.jpg

No ball, not even the "trip handle"; you had to hold the lever forward constantly.  When I inherited the tractor in the '80's, I figured I'd make it right.  Bought a used hydro handle with everything except (you guessed it) the ball.  However they were still available to purchase (part# 166178/2166178) so I ordered one.  

But before I installed the trip handle I measured the ball "just in case" - it's 5/16" diameter.  

Within a week or two, the new ball disappeared into the lawn so I'm back to holding the hydro handle when using the tractor (it becomes habit).  

I don't know exactly what is bent that allows the ball to fall out.  Maybe it's the hydro handle?   I didn't change that out.  

Good luck getting it to work.  If you do, let me know how you did it.  

 

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Yeah mine looks pretty much identical to yours. Definitely a pain, thanks for the info. I will try to make something to make it better and will post the solution if I come up with one 

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