# Briggs and Stratton no spark



## raywel (Apr 22, 2015)

Hey all,

Very new to the forum and to small engine repair. I have a Murray rider with a B&S 12.5 HP motor. I pulled it out this year and it won't start. Tried a few things that I found on the web. Here is my breakdown.

1. Poured a little gas in the carb - didn't start
2. Replaced the spark plug - Didn't start
3. Grounded the spark plug to the block - No spark
4. Used sandpaper on the flywheel and armature - didn't spark
5. pulled kill wire - SPARK!!!!

Im imagining that its none of the switches (clutch, seat and blade) because the engine would turn over.

I pulled the kill wire and visually inspected it and it looked to me like it wasn't damaged. It goes into a coupler and turns into a Yellow wire which I imagine goes to the ignition so I can actually turn off the motor.

Im stumped here. I don't know what to do next. Any help is appreciated!!

Thanks
Ray


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## MPR (Aug 28, 2010)

This site may have a wiring diagram:

http://www4.briggsandstratton.com/m...rical from MA-S-1612 2004 Quick Reference.pdf


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## AVB (Nov 28, 2014)

Okay your ignition system on the engine is fine. Your tests has cleared that part.

Disconnect at the connector the coil kill wire meets with the yellow wire and see if the problem still exists at this point. If does then there is a short that lead on the engine. If it doesn't then it most likely the operator seat switch or a short in the wiring. Mice are great at chewing wire insulation off.

If doing the above and the problem went away then it is now a mower wiring problem and you may need the wiring diagram for it. Also it helps to have DVMM, ohms meter, or test light for checking for shorts.

The operator switch is not part of the starter circuit; just an engine kill circuit. The PTO, Brake/Clutch and ignition switches are the only ones that in the circuit. The magneto kill circuit the seat, the PTO (engaged) and brake/clutch (Released) switches. The PTO and brake/clutch switched kill circuit is disable when the operator switch see the operator is on the seat so the seat switch is the main line of defense in this area.

One thing to remember is that depending the age of the Murray you can not simply unplug the seat switch as it may contain a built-in shorting strip. You can't simply jumper it either which what the shorting does when it unplugged.


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## raywel (Apr 22, 2015)

Guys,

Thank you for the replies.

AVB, I didn't understand everything you posted but I will go over it a few times and give it a try. Im sure I will post more when I know more.

Thanks
Ray


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## AVB (Nov 28, 2014)

Ray, If you post the Murray's model I'll see if I can find a wiring diagram for you.


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## raywel (Apr 22, 2015)

AVB,

Thank you.

Model number of the Murray is 387002X92
Model number of Briggs is 21A7070223E1

This AM I tried unplugging the coupler of the kill wire to the yellow wire and there was a spark so if I understand you correctly that tells me that the issue is not with the black kill wire being grounded but with a wire from the coupler being grounded. Lucky me as those are harder to reach. 

So would a recommendation be find any issue with the wire and use electrical tape or just try to order the entire harness?

Im not totally sure what the wiring chart will give me, but that's only because Im not an electrician.

Im confused on one thing you said. You mentioned that the operator switch is not part of the starting circuit just to kill the engine. If that's the case why would that be an issue for no spark?

Thanks again so much.
Ray


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## AVB (Nov 28, 2014)

Found the wiring for the 387002X92 depend if is a 2004 or 2005 as which seat switch connector it has. The '05 has the connector that shorts itself as if the operator is not seat if is simply disconnected. Other that the wiring is as simple as can. 

Only two switches that give problems the seat and the ignition. Whole yellow wire is a grounding type circuit so any bare wire area that touches the frame will kill the engine. 

Yes electrical tape will do but it better to cut out the bad section and a new section using insulated solderless connectors.

Also check the wires as they go behind the starter. I have had several in the last years where the starters were replaced and the wires got pinched between the starter and the crankcase causing shorts.


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## raywel (Apr 22, 2015)

AVB, 

Thanks so much. So just so I focus on the right area, you mention this seat switch. If that is faulty will that cause the plug to not spark? I can check that easily with a meter tonight. How would I know if the switch is an 04 or 05? Is there a part number on the switch? If that seems to be bad, can I disconnect it and still turn the engine off with the key? If its the 04, how would I bypass it just to see if that's the issue?

As far as testing behind the starter, I don't believe that is an issue because when I unplugged the coupler the engine had spark and that was the black wire running behind the starter.

Thanks
Ray


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## raywel (Apr 22, 2015)

AVB,

One last question, for now. I thought the seat switch didn't come into play for a spark so am I right to be looking at the switch?


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## AVB (Nov 28, 2014)

raywel said:


> AVB,
> 
> One last question, for now. I thought the seat switch didn't come into play for a spark so am I right to be looking at the switch?


To shut down the engine the coil control terminal must be grounded which kills the spark. Normally you this by turning the ignition off but as a required safety measure manufacture's use the seat switch to also do this in case the operator is no longer in seat such being knockoff or falling 
The following is the wiring diagram for '04 model.


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## AVB (Nov 28, 2014)

raywel said:


> AVB,
> 
> Thanks so much. So just so I focus on the right area, you mention this seat switch. If that is faulty will that cause the plug to not spark?


Yes


> If that seems to be bad, can I disconnect it and still turn the engine off with the key?


Yes

When checking the switch itself with an ohm meter it will read shorted (closed) when no operator is on the seat; open when it is depressed. 

Both the '04 and '05 switches are the same; it the connector that is different. '05 connector has shorting strip in it that will short the two wires together when disconnected. To bypass the '04 seat switch you simple unplug it. The '05 requires you to clip one of the wires at the connector.


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## raywel (Apr 22, 2015)

AVB,

Thank you... thank you... thank you!!!!

I can't explain it but I disconnected my seat switch and the switch was working. I cleaned the leads and then cleaned in the coupler as best as I could. When I put it back on I had spark. I put the whole thing back together and it works like a champ. Now I will change the oil and this baby should be all set.

Thanks
Ray


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