Kubota L4400 - Cranks but won't start, blows "Key Stop" fuse every time

Jon D

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Equipment
Kubota L4400
Jan 22, 2023
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0
1
Australia
I replaced the battery on my L4400 with one that had opposite polarity. Of course it blew my slow blow fuse. In a moment of historical stupidity, I pulled the fuse and placed a wire across the slow blow fuse terminals to try to override it (no access to replacement fuse at the time). Once I realised the error of my ways I got replacement fuses and the correct battery. Now the Key Stop fuse keeps blowing every time I try to start it. I've replaced the fuel stop solenoid, glow plugs and glow relay and it is still blowing the Key Stop fuse. Anyone know what could be causing this?
 

Mark_BX25D

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Bx25D
Jul 19, 2020
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Ouch.

A fuse that blows immediately is the result of a short circuit. At this point, you must resist the urge to "do SOMETHING!". You risk doing more damage if you get it wrong.

First I suggest you get a multimeter and a test light. You can't keep just blowing fuses as you search for the short. If you make some jumpers to connect where the fuse goes, you can attach your test light in place of the fuse. Then as long as the light is on, your short circuit sill exists. Once you find and correct the short, the light will go out.

Next, get a wiring diagram for your tractor. There's a site where you can download free Workshop Manuals (WSM), in PDF format. It's very helpful to print out the relevant pages, then you can use a highlighter to highlight the circuit you are working on.

But.... dummy me doesn't remember the site. Do a search here on "WSM" and you should find it, or maybe somebody will come along and post a link.

While you are waiting to get the manual, it won't cost anything but time to get a flashlight and start looking for melted wiring.
 

Dave_eng

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M7040, Nuffield 465
Oct 6, 2012
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I replaced the battery on my L4400 with one that had opposite polarity. Of course it blew my slow blow fuse. In a moment of historical stupidity, I pulled the fuse and placed a wire across the slow blow fuse terminals to try to override it (no access to replacement fuse at the time). Once I realised the error of my ways I got replacement fuses and the correct battery. Now the Key Stop fuse keeps blowing every time I try to start it. I've replaced the fuel stop solenoid, glow plugs and glow relay and it is still blowing the Key Stop fuse. Anyone know what could be causing this?
Likely OPC control/timer. Operator Presence Controller. It is the master brain sent info by various safety switches.
forum L4400 opc.jpg

The following description is not for your exact model.

forum L3400 opc timer description.jpg


forum L3400 opc checking.jpg

I do not have the WSM for your tractor. Call Messicks to be certain your model has this part.

Dave
 
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North Idaho Wolfman

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L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
Jun 9, 2013
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Get the WSM (aka Service manual) it will point out how to test it.
I sent you a link.
Sounds like you have fried the OPC timer, that controls the stop solenoid, there may also be a relay for it too.
Other part that could of very well be fried will be the alternator.

Dave posted up all the details that will also be in the WSM.
 
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