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Snapper M301019BE / B&S 28b707-22153-E1 spark / electrical issue

batesman's Avatar

Join Date: Jan 2010
Posts: 5

10-19-14, 04:59 PM   #1  
Snapper M301019BE / B&S 28b707-22153-E1 spark / electrical issue

Hello All,

I have a Snapper M301019BE with a B&S 28b707-1153-E1. On this mower, there are 3 safety switches: one under the seat, one at the blade deck, and one that checks to see if the brake / clutch is engaged. In addition, these switches route to an interlock module (a transistor) opposite the battery compartment.

When I got the mower, I had no spark. I disconnected the coil wire from the magneto shorting block which bypassed all of the safety systems. I got spark. I tested all of the switches and got continuity when and where I should. This led me to believe that the interlock module was faulty, so I replaced it.

From the starter key switch, there are several wires that run out and branch to the starter solenoid, and interlock module, as well as one lone green wire that was cut/broken at the end, that runs all the way to the engine (I believe this wire is a ground though I see no evidence of where it was connected). I put a new ring terminal on it and connected it to the engine ground. From the engine ground, there is also a green wire jumper that connects to the magneto shorting block. So I have a green wire (ground?) running from the ignition key switch, to the engine ground, then jumpered up to the magneto shorting block.

What is happening now (what I am trying to figure out) is that with all wires reconnected to the shorting block, I get no spark. When I remove the green wire jumper (jumping the shorting block to the engine ground) the engine runs, and also turns off using the key as it should - however, this also appears to bypass the safety switches, as I am not activating the seat switch during the start process. I tried moving the green wire that runs from the ignition switch from engine ground up to the shorting block (leaving the green jumper in place bridging the shorting block and engine ground), but that didn't make any difference.

It is clear that the green wire is shorting the circuit when I connect it to the shorting block, but I don't know why. I also don't know why, when removed, it bypasses the safety system. Any thoughts on this?


The wiring diagram is here: SNAPPER Rear Engine Rider Electrical (for electric ... Parts | Model M301019BE | SearsPartsDirect

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marbobj's Avatar

Join Date: May 2006
Posts: 3,658

10-19-14, 05:37 PM   #2  
All your safety switches as well as the engine ignition switch has to have access to ground, which is the green wire. If the engine shuts off with the key, and your green wire disconnected, then you have another keyed ground to the engine module (coil).

As far as the safety switches, disconnecting the grounding wire to the block would take those switches out of the equation and the engine would start and run.

Small engine ignition systems that aren't battery fed kill with ground. Those that are battery fed (few and far between anymore) kill by cutting the power to the ignition. The older Kohlers with the point/condenser fall into the latter. I can't think of any current systems like that now. Most have the ignition module which runs on open circuit to ground and kills with the closed circuit to ground.

cheese's Avatar
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Join Date: Jul 2001
Posts: 16,567

10-19-14, 06:59 PM   #3  
I have found through experience that the interlock module can be fooled by electrical feeding through moisture. If any of the switches or connectors are wet or have dirt and wet grass packed in them, it can cause it to switch the ignition off. If this is not the case, I would be suspecting the interlock module... are both of them behaving the same way?

"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

batesman's Avatar

Join Date: Jan 2010
Posts: 5

10-19-14, 10:50 PM   #4  
Hi Cheese,

I cleaned all electrical connections with contact cleaner and then applied dielectric grease. None of the connections were corroded or gummed up. I do not think that both modules are behaving the same way because the green wire from my ignition key switch was not connected to anything during my initial tests. I can swap the modules to verify though. Prior to replacing the interlock, I only had spark with the coil ground wire disconnected from the magneto shorting block.


Based on the wiring diagram, the black wire from the ignition switch goes to the magneto shorting block. I think that is the secondary keyed ground in question. The red and blue wires route to the solenoid and the mystery green wire isn't even pictured!

I am going to call snapper later today and see what their techs have to say.

batesman's Avatar

Join Date: Jan 2010
Posts: 5

10-20-14, 05:08 PM   #5  
I called Snapper today and got the lowdown. The green wire should be connected to the engine ground - it grounds the ignition switch case. The black wire from the ignition switch goes to the magneto shorting block. There should not be a jumper wire between the magneto shorting block and the engine ground.

Additionally, the reason that the safety systems did not appear to work properly is because the interlock system functions not by monitoring the condition of one switch, but by monitoring the condition of all switches in relation to each other. The previous owner bypassed the brake/clutch switch by bolting it to a piece of aluminum bar stock which permanently depresses the button on the back of the switch. Because this switch is bypassed, the safety system appears to assume that the rider has the brake/clutch engaged - even when no rider is present. Therefore, the safety system always assumes that an operator is present on the mower.

I may change it back, but I like the ability to bend over and pick up sticks without the mower shutting off.

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