B7800 blowing 5A start/stop fuse, solenoid ok

[Ray7800]

Good morning and thanks for all of the support in these pages.

Short version - while driving the tractor to a neighbor the engine stalled. The starter wouldn't engage and when jumping the terminal posts it would roll over and the tractor wouldn't start. Upon inspecting the fuses, the 5A was blown. Replacing it and turning the key blows another. Disconnecting the "fuel shutoff" solenoid and the fuse stopped blowing, so I replaced the solenoid (silly me, $152 later) and the problem persists. I am looking for a wiring diagram and while I search I thought I would rely on your expertise.

BTW - it runs with the fuel shutoff solenoid removed & disconnect, starter operates, etc. Everything normal (except shutdown means you depress the plunger).

Thanks everyone!

Ray
B7800 with a few cool attachments.

 

[N3BP]

You might want to double check the manual on fuse size. 5A seems small for solenoid.

 

[Edke6bnl]

this is some talk on fuel shutoff solenoid that might help that I save for my B7800

 

[GreensvilleJay]

curious, so I just downloaded the op man from kubotabooks.
5A is correct rating/value/size for fuse
I don't have wiring diagram but..

question. is there ANYTHING else connected to that 5A fuse ?

also, disconnect solenoid and use ohmmeter to measure it's resistance. be sure to subtract 'zeroed test leads' value.

 

[Ray7800]

You might want to double check the manual on fuse size. 5A seems small for solenoid.

I did verify, I also tried a larger fuse so I am convinced that somewhere in the circuit is a short or draw abnormally high

 

[Ray7800]

So, I am headed out to measure the resistance of the solenoid coil (both the original and new) and will report back. I think the fuse on the diagram below - just above "2" (key stop solenoid) only feeds two components. My little brain is saying if I replaced & verify "3" then it must be "2" and that seems more challenging to access. BOTH measure 16.2 ohms ***

I don't think there can be much more - except a chewed wire as opposed to a faulty component

 

[GreensvilleJay]

hmm.. somehow when you connect the stop solenoid, it's shorting the +12 'feed' to ground since the 5A fuse ONLY blows when it's connected.

If solenoid read 16 ohms, it's 'good' should only draw about 1 amp of current so won't blow 5A fuse.

it is a bit of a puzzler so carefully inspect that wiring. A picture of two might help.

 

[Henro]

Here is the electrical diagram for the B7800 which is from the supplement to my B2910 WSM.

Looks like the fuel cut off solenoid is powdered through a 30 Amp fuse, and the 5 A fuse feeds the controller module, which energizes the coil of the relay that activates the fuel cut off solenoid.

Something doesn’t equate with the description of events the OP posted…

 

[GreensvilleJay]

His diagram isn't for the b7800.....sigh.......

 

[Henro]

Looking at the electrical diagram for my B2910, The fuel cut off solenoid is powered by a five amp fuse.

The B7800 came out after I bought my B29 10. The B7800 is basically the same tractor without the deluxe features of the 2910.

I’m wondering now if the OP’s tractor might have been one of the first 7800s, and if it could have the same wiring as the 2910?

The B2910 does not have a controller module. I’ve read that during model transitions, some of the last units in the production run may be given the electrical circuitry of the new models. Perhaps the opposite is true as well? Just speculation... If the OP 7800 doesn’t have a controller module that would tell us something. I don’t have a clue where you might look to find that physically.

 

[Ray7800]

Here is the electrical diagram for the B7800 which is from the supplement to my B2910 WSM.

Looks like the fuel cut off solenoid is powdered through a 30 Amp fuse, and the 5 A fuse feeds the controller module, which energizes the coil of the relay that activates the fuel cut off solenoid.

Something doesn’t equate with the description of events the OP posted…

View attachment 134353 View attachment 134354

So, I can take photos but all you see is a connector, a fuse box, etc. What I did do is probe a bit looking for a short - testing the "Stop Solenoid" connector to ground I didn't detect a short. I replaced the fuse, turned the ignition on, and don't seem to get 12 volts. Looking more carefully at the schematic, the 2RW wire connects to the key switch, seat switch, and HST switch. That would imply a short to one of those switches, but I can't figure out why connecting the solenoid would make any difference.

I also measured both sides of the fuse (to ground) - 12 volts on one side (with key on), open on the other. puzzler.

Could it be something to do with the controller?

Saw the reply, thanks. I'll have to remove the shroud to see the other components.....

 

[Ray7800]

His diagram isn't for the b7800.....sigh.......

Which he (which diagram is good, which is bad)?

 

[Henro]

So, I can take photos but all you see is a connector, a fuse box, etc. What I did do is probe a bit looking for a short - testing the "Stop Solenoid" connector to ground I didn't detect a short. I replaced the fuse, turned the ignition on, and don't seem to get 12 volts. Looking more carefully at the schematic, the 2RW wire connects to the key switch, seat switch, and HST switch. That would imply a short to one of those switches, but I can't figure out why connecting the solenoid would make any difference.

I also measured both sides of the fuse (to ground) - 12 volts on one side (with key on), open on the other. puzzler.

Could it be something to do with the controller?

Saw the reply, thanks. I'll have to remove the shroud to see the other components.....

I think the first thing you need to do is verify whether you have a controller module or not. The drawing that shows the controller module shows the 2RW wire feeding 12 V directly to three fuses and not connecting to anything else. (5, 10 &20 amp) With the five amp fuse feeding the controller module.

Very difficult to troubleshoot a problem if the drawing you’re using doesn’t match the hardware you have…

edit: I know from reading posts here in the past that the B 7800 does normally have the controller module and The B2910 dose not. Since I have a B-2910 this caught my interest previously.

 

[North Idaho Wolfman]

How many wires feed the solenoid, and what color?
Not how many are at the plug as it will have 2 wires spliced together, but then that will tell you too if both wires are white.

The most common issue is the HST switch, next will be the seat switch and lastly the OPC controller.

 

[N3BP]

I think the first thing you need to do is verify whether you have a controller module or not. The drawing that shows the controller module shows the 2RW wire feeding 12 V directly to three fuses and not connecting to anything else. (5, 10 &20 amp) With the five amp fuse feeding the controller module.

Very difficult to troubleshoot a problem if the drawing you’re using doesn’t match the hardware you have…

edit: I know from reading posts here in the past that the B 7800 does normally have the controller module and The B2910 dose not. Since I have a B-2910 this caught my interest previously.

I'm with ya. The B7800 appears to be a B2910 with all the operator presences stuff incorporated into it. I had a chance to study the wiring diagram and the 30A is definitely what protects the solenoid, and the 5A for the controller.

What I'm wondering is if the controller was damaged when the OP tried to jumper out the starter solenoid, which the manual always tells you not to do......

 

[Ray7800]

So, I started to pull the black plastic cowling off (still struggling). I ran a few tests - sometimes it runs, sometimes it pops a fuse when the key turns to on (no started or glow). I am growning convinced a critter got to my wires - if I could see in there

 

[Henro]

From your description, it does sound like there could be a wiring issue for whatever reason.

It would be good if you could verify for sure what wiring your tractor actually has, and thinking about it, I’m gonna guess it’s probably the B7800 wiring.

One easy way to determine this would be to do what the Wolfman suggested above, and look at the wire colors going to the fuel cut off solenoid. I don’t have the drawings in front of me right now, but I believe I remember that one wiring harness has two wires the same color and I think they’re white. Also, I kind of remember that the other one has two wires that may be different colors (not white), and I think one of them is red with perhaps a tracer or not, I can’t remember but mainly red.

This information would be important because it could tell us what wiring diagram applies to your tractor for sure. If you don’t mind doing it, could you take a look at the wires going to the fuel cut off solenoid and see what color they are?

 

[GreensvilleJay]

Chasing down electrical 'gremlins' can/is/will be a lesson in futility......Not KNOWING what colour wire goes where and what it does become very,very frustrating !!
Hopefully ,Kubota used a colour to be the SAME for all models.like 'black' is always a 'ground'.
Perhaps some nice soul can add their B7800 wiring diagram into the 'electrical section' ?

 

[Henro]

Chasing down electrical 'gremlins' can/is/will be a lesson in futility......Not KNOWING what colour wire goes where and what it does become very,very frustrating !!
Hopefully ,Kubota used a colour to be the SAME for all models.like 'black' is always a 'ground'.
Perhaps some nice soul can add their B7800 wiring diagram into the 'electrical section' ?

I did post the wiring diagram for the B7800 in post number eight. But it does not indicate that the fuel cut off solid is fed by a five amp fuse as the OP indicated in one of his initial posts. That’s why there’s a question as to the wiring on his tractor.

My guess is that his wiring is the B7800 wiring but there’s always the possibility it could be the B2910 wiring. That’s why he needs to verify somehow what the wiring likely is, so he can get good advice from people here able to provide it.

 

[GreensvilleJay]

OK, using the diagram in #8, it clearly shows that the 'solenoid' power is from a 30 A fuse NOT a 5 amp. It's fed through a 'key stop relay'. ,the ONLY thing on that 30 amp fuse.
I'm wondering if he's just misreading which fuse goes where ? perhaps the fuses aren't physically in order, as per the wiring diagram ??
30A fuse will be green
5 A fuse is brownish