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Discussion Starter #1
Hi everyone. This Snapper mower (28085) has a motor (12 hp) replacement on it. The 12 hp motor must have come off another brand mower. The ignition switch (5 stud)/wiring harness is hooked on mower. It will only start by shorting
starter stud. The 5 stud ignition switch(A,I,S,B,R letters on bottom) is hooked
up wrong to motor. I need help with the re-wiring for right hook-up.


THANKS,willie
 

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Each letter stands for something:

M - Magneto
L - Lights
S - Starter Solenoid
A - Accessory
B - Battery
G - Ground
I - Ignition
R - Regulator/Rectifier

You'll definitely need +12 going into your B terminal, and send juice down the S terminal to the starter solenoid. If there is a fuel knockoff, that generally powered on the A. R will of course go to your voltage regulator, assuming this engine has a battery charging system.

Just match up each system with an appropriate position (start or run) and you should be ok.

It definitely can be done, however you would be much better off matching the engine with an appropriate key switch. I personally would not spend the time tracing circuits and rewiring harnesses when I could grab the right one for around $20. I get mine from Stens.

http://www.stens.com

If you have any specific questions, let me know.
 

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Discussion Starter #3
Thanks for the input rther.
I will re-check & test every thing.
Will get back with results soon.


Thanks, wille
 

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Discussion Starter #4
How do I test the ignition switch unplugged from wiring /grounded to frame or not?


THANKS,willie
 

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Use your multimeter set to either resistance or preferably, continuity. My meter has an audible signal on the continuity setting. Attach one probe to B and probe the rest to find out whether they are on or off in the Run and Start position.

If you're just probing the terminals, it doesn't need to be grounded.
 

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Discussion Starter #6
Testing ignition switch in hand with multimeter set on continuity. (5 post)
(!) With B attached & in run position (other than S post) 3 post show continuity.
(2) " B " " " start " only S show continuity.
Is this a good switch or not?

THANKS, willie
 

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Testing ignition switch in hand with multimeter set on continuity. (5 post)
(!) With B attached & in run position (other than S post) 3 post show continuity.
(2) " B " " " start " only S show continuity.
Is this a good switch or not?

THANKS, willie
It sounds like the switch is good.

Earlier you said that the engine only starts by shorting the starter stud. Does it stay running if you do this? Does the key switch turn it off? Is the battery charging (if it has a battery)? If it does, you might be able to get away with simply attaching the starter solenoid wire to the S terminal.

If not, you either need to replace the switch or rewire it. In order to rewire it, you'll have to identify to which component each wire goes by checking with continuity. Once the wires are all labeled, it's simply a matter of matching ignition, voltage regulator, starter, battery, and fuel knock off to their respective terminals on the starter.

Before you start cutting any harnesses, I want to stress that it would be much simpler to purchase the appropriate key switch for the engine. Stens may not sell to end users, I don't know. You can call them at 1-800-457-7444 and they can at least give you a part number for a switch that will match your engine. There is probably a mower shop close to you that is a Stens distributor and either has it in stock or can order it for you.

It's totally up to you. If you want to go ahead and rewire it, I can walk you through further if you have any other questions.
 

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Discussion Starter #8
I found that the fuse (30 ampere?) was internally blown. What is the proper ampere? I put a 15 ampere fuse in the holder & turned switch to start. The engine turned over but did not start before blowing the fuse. What would cause this to blow? Are key switches grounded thru nut holding it to frame?

THANKS,willie
 

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I found that the fuse (30 ampere?) was internally blown. What is the proper ampere? I put a 15 ampere fuse in the holder & turned switch to start. The engine turned over but did not start before blowing the fuse. What would cause this to blow? Are key switches grounded thru nut holding it to frame?

THANKS,willie
I'm having trouble finding an electrical schematic for that machine, so I'm not sure how many amps the fuse should be. I found some parts diagrams, but they do not mention fuses:

http://www.partstree.com/parts/?lc=snapper&mn=28085+28%22+8+HP+Rear+Engine+Rider+Series+5

Machines I have repaired in the past took 20 A fuses. Keep in mind they are propane burnishers and not lawn mowers, but it's still a 12 V starter cranking a 17 HP engine so I would imagine the amp draw is similar.

As far as I am aware, key switches are grounded to the frame through their chassis and nut.

Before you install any more fuses, you will want to make sure the wire running from the S terminal on the key switch to the starter solenoid is not shorting against the frame. Visually inspect it.

With the key switch in the off position, set your multimeter to continuity. Connect one end to the wire leading from the key switch to the starter solenoid, and touch the other end to ground. You should have no continuity. If you do, the wire is shorting out.

If not, try a 20 A fuse. If that's not enough - and since it had a 30 A fuse when it was brought in to you - you might want to try a 30 A fuse.

I had a similar problem that was driving me crazy with an Onan Performer popping fuses. The starter would crank in the start position and continue cranking in the run position until the fuse burned out.

Because of the way the engine is wired, it requires a diode to be placed in the start circuit to prevent voltage leaking back from the run circuit. The diode was bad and allowed voltage to flow backward. Kind of unusual, but in the end it turned out to be a simple repair.

If there is in fact a diode on your machine, and if it is bad, you can usually find them hiding within the plastic tubing surrounding the wire harnesses. It's likely on the main bundle that leads up to the starter switch. They're wired inline, either soldered or plugged in.

If you have a diode and you'd like to test it, you first have to isolate it. Disconnect it from both wires. With your multimeter set to resistance, place one lead on each end of the diode. Now reverse the leads and repeat. You should have infinite resistance in one direction and very little or none in the other direction. If voltage flows both ways, or doesn't flow either way, the diode is bad.

I hope that helps you out some.
 

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Discussion Starter #10
I am back!!! I hope you do not get tired of helping people like me. I love to try & solve any
problem at hand. This electric schematic at partstree.com (281013BE-28"-10HP) is the wiring that closely matches this mower. I have the replacement key switch wired(#1) S wire to top clip of solenoid, (#2) B wire to right large solenoid post, (#3)I wire to magneto shorting block. The other 2 key wires (A&R) are not used.I tapped ends up. Starter motor wire is hooked to left large solenoid post.The(replacement 12HP)motor on the frame has a 2 wire connect coming from flywheel. One is for charging battery, other is for lights. The mower has no lights. One wire is missing from the double connect feeding out. The one wire feeding from dido that charges battery may have been plugged in backwards. The dido feeds one wire on that side of double hookup. Would that wrong connection cause the fuse to blow?
THANKS, willie
 

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I am back!!! I hope you do not get tired of helping people like me. I love to try & solve any
problem at hand. This electric schematic at partstree.com (281013BE-28"-10HP) is the wiring that closely matches this mower. I have the replacement key switch wired(#1) S wire to top clip of solenoid, (#2) B wire to right large solenoid post, (#3)I wire to magneto shorting block. The other 2 key wires (A&R) are not used.I tapped ends up. Starter motor wire is hooked to left large solenoid post.The(replacement 12HP)motor on the frame has a 2 wire connect coming from flywheel. One is for charging battery, other is for lights. The mower has no lights. One wire is missing from the double connect feeding out. The one wire feeding from dido that charges battery may have been plugged in backwards. The dido feeds one wire on that side of double hookup. Would that wrong connection cause the fuse to blow?
THANKS, willie
On the machines I have worked on, there are two wires coming from the charging coil because it produces AC voltage. These two wires are plugged into a three terminal rectifier. From the third terminal to ground, you receive DC voltage to charge the battery. The DC voltage should be half the AC voltage.

If DC is sent down the charging coil wires, it will toast the coil.


I did not see a wiring schematic on that website. I have attached an example schematic from another machine that can be used as a guide. This may be helpful to you because the key switch on this machine appears to be identical to the one on yours. Remember, this is from a propane burnisher and not a lawn mower, but the principles are basically the same.

 

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Discussion Starter #12
I finally put another key switch(5 prong/start= B+S, run=B+L, off=G+M) on that matches
magneto grounding block of motor. The L is not used as there are no lights. Fuse do not blow now.
The problem now seems to be equipment bind when cranking motor over. I will get back
after checking this problem.

THANKS, willie
 
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