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Intermittent Electrical issue with Craftsman Lawn Tractor 18.5 HP B&S engine


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10-18-10, 08:47 AM   #1  
Intermittent Electrical issue with Craftsman Lawn Tractor 18.5 HP B&S engine

Hi there. I have been having a battle with this tractor for some time. Model 917.273634. I looked through existing posts and did not find this same symptom. Anyone else have this?

Sometimes it runs fine, other times, it starts, but if I either let the clutch out (when in neutral) OR start the PTO, the engine dies. First I thought it was a carb problem, so I rebuilt and cleaned that. Then I also tested the carb solenoid. Did a test on the spark plug and determined that the electrical shuts down when that happens.

I can sometimes get it running again by disconnecting all the electrical connections and reconnecting them. With the help of Dad, we tested the ignition switch, the seat switch and the interlock switch. All tested ok. After re-assembly it ran fine - for about 20 minutes, then same thing. Turns on, but won't stay running.

I tried reasoning my way through this thinking, what items are related, electrically to both the PTO and the Clutch. The only items I can think of are the interlock and the seat switch. Am I missing something?

What should I replace? Those 2 switches? Anything else? Other tests? Thanks much!


Last edited by rdhamm; 10-18-10 at 09:03 AM. Reason: further information
 
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10-18-10, 11:32 AM   #2  
Sounds like the seat switch. You might find a little "button" of sorts on the switch that is activated when the switch is installed. If it is not making all the time, this could be the problem.
Normally the seat switch is the only one tied to both the clutch and PTO, as each requires an operator present (seat occupied).

 
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10-18-10, 02:09 PM   #3  
Thanks

I have had this switch out several times and every time that I test it, it works. Is there a way to bypass it to see if that solves the issue? I have tried leaving it unplugged and putting a jumper across the connectors, neither seemed to work.

Thanks again.

 
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10-18-10, 08:17 PM   #4  
You can't jump the switch, it has an internal switch in the connector that shorts it when it is unplugged. Take a zip-tie/cable strap and cinch the connector tight to the switch in a manner that keeps the connector pushed up tight. This should solve the problem. It's the internal switch in the connector that is giving the problems and this de-activates it.


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

God bless!

 
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10-19-10, 07:50 AM   #5  
bypass worked!

Thanks very much. I used the zip tie suggestion - I had to carve small notches in the side of the switch so it would not slip off, but the plastic is soft so that was easy.

So, cheese, is this internal switch, the one in the connector - is that in the body of the seat switch, or is that in the end connected to the wiring harness?

I am wondering if I need to replace both the seat switch and the wiring harness, or just the seat switch?

Thanks for all your help. At least I can use it to get that carpet of leaves off the ground. I will re-post here if the intermittent issue returns.


Last edited by rdhamm; 10-19-10 at 08:26 AM. Reason: emphasis
 
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10-19-10, 10:54 AM   #6  
The zip tie is a permanent fix, so you shouldn't have to worry about it anymore. The connector clip wears and flexes over time, allowing the switch inside the connector to disengage.


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God bless!

 
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10-19-10, 11:25 AM   #7  
Thanks again

cheese, I get that I can leave the zip ties in place if I want to bypass the safety mechanism. What would I need to replace if I want that safety measure in place? Is it just the switch, or is it the wiring harness too? I just don't know where that second, internal switch, is that you mentioned.

Could I replace the switch and just put spades on the wires to connect the seat switch too, if the wiring harness replacement is too difficult.

 
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10-19-10, 05:17 PM   #8  
Yes, you can do the spade terminal thing. I'm not sure what you mean about bypassing the switch. What I recommended doesn't bypass the switch. Did you zip tie the plunger down to the switch? If so, that is not what I was saying. It will probably fail again if that's what you did.


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10-19-10, 06:02 PM   #9  
Bypass

Cheese, perhaps we are not communicating as well as I thought.

I zip tied the plunger down on the switch. By doing this, the safety mechanism of ensuring that someone is in the seat is bypassed. You were not saying to ziptie the plunger down?

You indicated that besides the plunger on the seat switch, there there is an additional switch in there somewhere when you wrote:
"...it has an internal switch in the connector that shorts it when it is unplugged"
I understand that this switch is a normally off. I tried earlier to unplg it and jump a wire across the ends of the wiring harness. As I posted in my first post, that jumping failed. Now I take it to understand that there may be a second switch that caused that jumper to fail. I am trying to determine if that is the cause of the failure.

So, if I want to fix the tractor so the safety mechanism works, where is that other internal switch, is it in the seat plunger switch, or is it in the end that plugs into the seat plunger (part of the wiring harness)?

I do appreciate all the help. Thanks.

 
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10-19-10, 06:29 PM   #10  
It is inside the connector on the wiring harness. If you'll push this connector up tight to the switch and put a zip tie around them to keep it tight, it will hold this inner switch open as it should be. This inner switch in the connector is designed to engage if someone unplugs the seat switch to disable it, so as to eliminate someone "bypassing" the seat switch. When the clip wears and stretches, it thinks it's unplugged and shorts the circuit. Pushing it up tight and holding it tight with a zip tie fixes the problem.


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

God bless!

 
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10-20-10, 06:41 AM   #11  
depending on how it's wired maybe there is a bare wire in the circuit of the seat switch that sometimes gets grounded.

 
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