# Troy Bilt Trimmer TB475SS Won't Stop



## mikeinri (Dec 2, 2009)

OK, solved my tractor problem, now I have a new problem on another machine...

I have a Troy Bilt trimmer (weed whacker), model TB475SS. This unit is several years old, but is rarely used (maybe 10 times a year), runs and looks like new. I have the grass cutter attachment, a rototiller/cultivator attachment, and a brush cutter attachment. I use each of those a few times a year, never have any problems at all while it's running. Always starts right up.

The problem is that it refuses to shut off when the kill switch is pressed (I have to remove the spark plug to stop the engine). This actually started last year, I just never found the time to deal with it.

It's not "after-run," it's just as if the switch isn't being pressed.

This weekend, I tested the switch with a voltmeter, it seems to be fine [infinite resistance when in running position "I", closed circuit (0 Ohms) when in stopped position "O"]. I checked the wiring, found no cracks in any insulation, all connections appear to be normal. I tested the switch wires at the ignition module, got the same results when I pressed the kill switch.

I have a hard time believing that the ignition module would cause this. Does anyone here have a better diagnostic test?

Mike


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## mikeinri (Dec 2, 2009)

Any ideas?

I thought about pulling the switch out, running the engine and putting a screwdriver across the switch terminals, just to completely rule out the switch.

Mike


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## Basementgeek (Feb 7, 2005)

That would be one way I guess. 

BG


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## kjms1 (Jun 4, 2010)

> [infinite resistance when in running position ... "I", closed circuit (0 Ohms) when in stopped position "O"]



0 ohms means it is open circuit ... so if i am understanding what you are saying,,, that means when you depress the switch it is removing ground or power from it to kill it ... if your's is this way that means it is still getting its source from some place else 

Most kill switches are a open circuit and when you depress them it sends a ground to the ignition system or spark plug to kill it


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## mikeinri (Dec 2, 2009)

I'll check it again. I think it's working correctly, I may have just typed it backwards...

Let's assume for a minute that the switch and wires are OK. This unit has an extremely simple ignition system, what could cause it to keep sending juice to the spark plug if the ignition is shorted to ground with the switch?

Mike


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## kjms1 (Jun 4, 2010)

trace the 2 wires on the switch and see were they go


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## mikeinri (Dec 2, 2009)

kjms1, you may want to double-check your prior post. 0 Ohms is a closed circuit, no resistance, current is flowing freely. Just touch the voltmeter leads together, and you get 0 Ohms. Separate them, infinite Ohms (open circuit).

OK, let's try again... 

The wires go to the ignition module. The kill switch does not allow current to flow when the engine is running (at position "I" open circuit, infinite ohms resistance). When the switch is pressed, the engine is supposed to stop, but currently keeps running (at position "O" closed circuit, 0 ohms resistance).

I tested this at the switch, then at the ignition module (to rule out bad switch wires).

I also put one lead on the red wire at the ignition module, and the other on the engine block, got the same results (open circuit with switch at "I" / closed circuit with switch at "O"). 

This makes me think it's grounding correctly, now why is it still running???

Mike


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## mikeinri (Dec 2, 2009)

I think the reason this is so confusing is that the switch is normally open (spring-loaded to stay in the "I" position, with no current flow), which makes this seem counter-intuitive. Many other switches make a closed circuit at position "I", such as when you turn on a power strip.

Either way, I really think the switch and wires are working correctly, but the motor won't stop.

Mike


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## kjms1 (Jun 4, 2010)

If you took a jumper wire and went form the engine to the ing module and it doesnt kill it
(by passing the switch totally) that will rule out the switch and wiring ... there for that would mean the ing module is bad


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## mikeinri (Dec 2, 2009)

I'll try anything, but I'd like to understand how the ignition module could cause this.
Mike


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## kjms1 (Jun 4, 2010)

it cant much dif than a car ing module and they louse up all the time ... age and heat get to them and things inside start to melt (resisters) ... you might find a lawnmower shop that you can take the module to and they can test it for you


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## mikeinri (Dec 2, 2009)

Thanks. Weird that if it failed, it would let the engine run but not stop.
I'll do some more testing and report back.
Mike


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