OPC 5 amp fuse blows when HST pedal moves (B26)

[kenmac]

As I stated above the 5 amp fuse blows whenever I attempt to move tractor. At first it was just in reverse, but now is either direction. I have looked for any bare wires in vicinity of switch and found no visible issues.
Just as an fyi, I am mechanically able ( former diesel and hvac tech). I'm thinking the opc is the issue, but that is just a guess at this point. I haven't ohmed out the HST switch, but engine starts properly when in neutral position. Any ideas or suggestions? Thanks in advance.
Ken

 

[GreensvilleJay]

It sure sounds like the wiring near the pedal but without the wiring diagram it could be 'something' else...
Doing 'long distance' diagnosis requires a crystal ball. Hopefully someone can post the wiring diagram.
Blowing a fuse does say a 'short' is happening. Perhaps there's another switch further away from the OPC and when the pedal is moved THEN that allows the short to occour.

 

[PHPaul]

Neutral safety switch on the treadle pedal has shorted out. I've replaced mine twice now.

 

[kenmac]

You're correct in your analysis. I need to do more troubleshooting, but decided to walk away for a little while. I pretty much did put my fingers on all wires in the area and found no issues. It seems that when HST switch opens the short occurs immediately. I'm not familiar with the internal workings of the opc, so I don't know where or how voltage is present at any time. I know that most equipment of any industry develops tendencies and my hope is that someone here has ran across this before and can shed some light on it.

 

[Dave_eng]

The 5 amp fuse is protecting all safety switches. Here is the circuit diagram.

(10) AC Terminal Lead
(11) Independent PTO Lever
Switch
(12) Seat Turn Switch
(13) HST Pedal Switch
(14) Seat Switch
(15) Regulator L Terminal Lead

Just because the shutdown occurs when you move the HST pedal does not mean the problem lies there. It could be that the opc logic kicks in when a safety switch is unsafe but until the HST pedal is moved the unsafe condition is acceptable and the engine continues to run. For example, a pto switch being ON does not become unsafe until you get out of the seat.

Seat switches are the most common location for wiring damage and especially since you have a backhoe.

Dave

 

[kenmac]

Thank you PHPaul. I hope you are correct I'll jump around the switch in the morning to confirm.

 

[kenmac]

Thanks to you also Dave_eng. I'll have to jump out other switches until defective one is found. I hope it's not the opc.....$220.
I do have the WSM.

 

[Dave_eng]

Thanks to you also Dave_eng. I'll have to jump out other switches until defective one is found. I hope it's not the opc.....$220.
I do have the WSM.

Taking the time to study this OPC logic table may give you some clues if, as I suspect, the HST pedal switch is not the cause but rather just a required condition to shut down the engine.

Dave

 

[lugbolt]

i've had a couple of those tractors do that and both times the switch itself was failed

 

[kenmac]

Thanks Lugbolt. Do you know a way to definitely determine the switch as the problem. Since it goes through the opc, I don't think it can be just jumped out and left that way can it?

 

[lugbolt]

look at the wsm in how the switch operates and you can test it from there

 

[GreensvilleJay]

for the pedal switch to blow the fuse, it'd have to connect to ground the lead going to the 'f' terminal of the OPC.
I suspect the switch might do this internally ? Say the 'f' side connects to the mounting screw ??
Maybe when installed ,it's overly tightened, cracks the plastic and metal gets real close to touching. Over time and vibration and use.... the cracked plastic fails and allows the short to occour ?
Would need to see picture of the switch or have one in my hand to see 'how-it-works'.

 

[kenmac]

Here's a little update on what I found this morning. The HST switch makes and breaks but doesn't break until pedal is depressed almost fully, so I will replace it. However I also found the one of the wires connected to the switch shows grounded. According to the diagram there should not be a ground wire in this circuit, so I think that is my problem. Now I have to check the wire at the opc connector and go from there. Unfortunately, that will have to wait until Monday. Is there any other way to access the opc without removing the steering wheel to remove the cover piece? I want clear access so I don't inadvertently damage something due to not being able to see clearly.

 

[whitetiger]

The simplest test is to unplug the harness from the switch, plug a jumper wire between the 2 harness terminals and drive the tractor around. If the fuse blows, you have an electrical system issue, and if it does not blow as usually is the case, the switch has failed.
Here are the tests for the switch.

 

[S-G-R]

Did you find a solution to your problem?

 

[kenmac]

Sorry for the delayed response here, but family for the Thanksgiving holiday and other issues arose. The story continues by me tracing wires looking for the source of the ground when the ground disappeared and all was well, or so I thought. After putting tractor back together I used it for about 30 minutes and thought it was good to go. The first time I really needed it, the fuse blew again. This time I was able to confirm the issue was the HST neutral switch itself. I replaced it today and put about an hour on the tractor. So far, so good! We shall see.
Thanks to all for your help. I learned a lot about my tractor, but would rather have not needed to learn it.

 

[S-G-R]

Glad you were able to get it resolved.