Electrical problems-Kubota

[Hunters gun]

My M135X has a small digital display on the right side of the cabin, separate from the one on the dash. Primary use of the display is a digital readout of the PTO RPM.
After years of no issues, 2 days ago, it went dark. Figured it was a fuse, and I was right (well sorta). I replaced the 5 amp fuse and it worked all day.
Today, started it up this morning to feed hay to some hay and it went out again. Replaced that fuse and it worked for a few hours. I knew I had a problem at this point. Replaced another fuse and it worked for about 1 minute. Next fuse snapped immediately.
Took the right side plastic console cover off and looked for mouse chewed wires, water corrosion leaks, bad connectors, etc. But there was nothing wrong.
Looked at fuse block and all looks well, too.
So I’m at wits end with it.
Wondering if the display itself could be blowing the fuse? Like the circuit board in the display itself has a short? The way the fuses started out lasting a day, than a few hours, then a few minutes, then instantly popping is the only thing that seems different about this one.

Thoughts?

 

[DustyRusty]

Check for a corroded wire terminal that is causing it to draw excell current. Bad connections will do that every time. If everything else is good, then it might be a bad circuit board, but if that is the case, then you wouldn't be alone, and others will also have had the problem.

 

[GeoHorn]

Check for scuffed/broken/intermittent ground on the harness between the display and the main dash and between the display and the PTO sensor.

 

[Roadworthy]

If the display works normally with the new fuse - for whatever period of time - the issue is probably not the display itself but circuitry going to whatever it is sensing. That fuse is providing power for the sensor line, too. You may be able to disconnect things one at a time to see which is causing the fuse to blow. You could also try putting an ammeter in series with each circuit to locate the source of current draw.

 

[Jchonline]

You could also run a brand new wire (splice it in, not permanent) to the fuse box so you can tell if it is wiring or not.

 

[Hunters gun]

So I disconnected the display from the harness, put a new fuse in, started the motor and it immediately blows the fuse.
So it ain’t the display.
PTO doesn’t need to be on to blow fuse, either. Just energize the fuse box and it’s toast.
Wiring looks good. No signs of mice, droppings, nests and no signs of water infiltration

 

[GreensvilleJay]

hopefilly you'e got an accurate wiring diagram for your tractor. without it, it WILL be a NIGHTMARE to trackdown the cause of the 'short'.
?? does it blow a fuse IF you do NOT start the engine ?

 

[Hunters gun]

No it does not blow a fuse if sitting there not running. Does not blow fuse in Accy position either. Fuse blows when in ignition position.

 

[GreensvilleJay]

Ok, so now you'll need to look at the schematic, follow the power from the 'run' pole of the sign switch and see what is connected to the fuse that keeps blowing.
without the schematic, i can't really help more.

 

[Hunters gun]

Purple wire with red tracer is the one that goes all the way to fuse block. I was thinking same as you, but there’s 6 wires leading to the plug at the display. What if one of those wires (say the one that reads PTO speed for example) is also energized by the key on switch and is damaged? This could also blow the fuse.

 

[kubotafreak]

Sounds like that power wire is grounding out. You need to make a fuse powered light. It is light bulb with two spades that fit in the blowing fuses terminals. The light will illuminate if there is a short. You are then able to move the harness until the light goes out. It helps narrow down shorts when you have no clue where to look on the harness.

 

[GeoHorn]

Sounds like that power wire is grounding out. You need to make a fuse powered light. It is light bulb with two spades that fit in the blowing fuses terminals. The light will illuminate if there is a short. You are then able to move the harness until the light goes out. It helps narrow down shorts when you have no clue where to look on the harness.

That is a pretty cool idea about the test-light…. The light-probe suggested earlier will accomplish that also. Clip the alligator-clip onto an un-coiled paper-clip and stick the paper-clip tip into one side of the fuse-holder and the point of the test-light onto the other…and VOILA!
This will work on a SWITCHED appliance only…. IF the switch is in the OFF position.

Unfortunately it’s not a fool-proof method of testing for a shorted-wire on unswitched circuits (such as this one being discussed)…. because it will also illuminate the lamp if the appliance itself is internally grounded/shorted….and the blown-fuse itself already told you the circuit was shorted.

 

[kubotafreak]

Agreed not fool proof, but didn't he mention he unplugged the circuitry/appliance? So the short was still in the harness?

If the harness is shorted after the fuse, this test is relevant. The flow path from the fuse box to the short is reversed to a ground leg. The light becomes the load, and your trying to extinguish it. (he will need the Koeo)

 

[Hunters gun]

Sounds like that power wire is grounding out. You need to make a fuse powered light. It is light bulb with two spades that fit in the blowing fuses terminals. The light will illuminate if there is a short. You are then able to move the harness until the light goes out. It helps narrow down shorts when you have no clue where to look on the harness.

I had one of those years ago I soldered together. It does work, but the problem is there are several wires (6) that could be shorting and the harness takes many twists & turns, intersecting with other harnesses.

Update: today, I went to the back of the tractor above the 3 point, under the cab. I noticed a plug that I believe senses the PTO. I unplugged it. Looked fine. Behind the plug there was 4 exposed wires for about 1-2”. They were unsheathed and untaped. They were rubbing at a 90* angle to a steel assembly. However, they were not really bare, just scuffed a little. I pulled the wires away and went back to the fuse panel. Inserted a 5A and fired the beast up. The display came to life and stayed on a good 10 minutes. I sheathed the wires in plastic loom and jiggled them. Fuse still holding. Started and killed tractor ignition a few times. Only had a few minutes to mess around with it, so I am by no means convinced I fixed anything, but today was better than yesterday.