Please Help! My B7800 is blowing a fuse, shutting down. Tractor stuck outside :-(

[easygo]

My B7800 is 13-years-old with 1100 hrs. The tractor shut down after I used it for two hours. I found the 5 Amp fuse that protects the key switch was blown. I replaced fuse, turned on the engine and it shut off after a couple of seconds. Same fuse blown. The third fuse didn't even operate the fuel shutoff solenoid, but blew as soon as I tuned the key.
I unplugged the fuel shutoff solenoid and replaced the fuse again. It didn't blow, so I thought I found the bad part.

Off to the dealer, bought new solenoid and a fuel relay, there goes $100. Replaced both and the tractor started right up. It ran fine for 10 minutes than started sputtering as if only running on 3 of the 4 cylinders. Sounded like the engine was not getting enough fuel. Eventually it shut off and now it is blowing the same 5 Amp key switch fuse again.

I have an old battery. Could the low voltage cause some isse like this?

It is rather cold here (-8 at the moment) Could that be causing any issues with the electrical system?

It is not the fuel. I use Power Service in every drop of fuel that goes into the tractor.
Any pointers would be greatly appreciated.

 

[diesel85]

It's probably a wire with the insulation worn and grounding to the frame.

 

[LouNY]

If you need to move it, disconnect the solenoid and physical move the shutoff to the run. But it sounds like you have a wiring problem to the key or from the key to the various relays or lights. Without a good wiring diagram it will be difficult to determine where or what.

 

[easygo]

I forgot to mention. The lights and the hazard flashers both work. The safety switches are ok to the best of my knowledge.

 

[Fallon]

Trace out the wiring on that circuit & look for a short. It could be a bad switch too, but less likely.

A bad ground would cause things to not work, but wouldn't blow fuses.

 

[sixdogs]

Have you searched this site for anything similar? I recall a mention of something like this before.

 

[easygo]

If you need to move it, disconnect the solenoid and physical move the shutoff to the run. But it sounds like you have a wiring problem to the key or from the key to the various relays or lights. Without a good wiring diagram it will be difficult to determine where or what.

Thanks LouNY. Unfortunately the solenoid moves something inside the injector pump area and there is no way I can manually set that to run.

 

[easygo]

Have you searched this site for anything similar? I recall a mention of something like this before.

That was the first thing I did. I found threads about no start issues, but none that listed a blown key switch fuse as part of the problem. Most were related to bad safety switches on the tractors. I wish mine was having symptoms like that. At least I would know where to start looking.

 

[Leejohn]

For a short I would check for a bare wire were the harness goes from fire wall to engine. The harness is real tight there and hitting the bell housing.

 

[fishpick]

I had a wire get worn bare under the tractor by the fuel pump that would short and kill the switch every time i tried to crank it...
electrical tape got me back to the barn...
paint on electrical tape solved it for good...

 

[Leejohn]

When I split mine I don't recall any wires running under the B7800.

 

[easygo]

So, I have the tractor fixed for now. Thank you all who responded to the question. The brief description of the "repair" went like this. I spent two thankless days trying to find the problem standing outside in the 0F weather 20ft from my barn, where the tractor broke down. Eventually with the help of a friend/neighbor we towed the tractor to his heated garage.

As it turns out the 5 Amp fuse connects to about a dozen or so things on the tractor. It was a royal pain in the aft end. First we checked the key switch, the wires to all the safety switches, replaced the fuel solenoid and the solenoid control relay and even took off the fuse box to look for a chaffed wire. I also took off the dashboard to look for mouse damage.
After not being able to find an actual short I decided to hot-wire all the safety switches to eliminate any potential problems. Yes. I could have tested the switches with a multimeter, but they are and absolute nightmare to get to, so I went the hot wire route.

At that point I decided to see what it does if I try to start it. The tractor would not start, but it didn't blow the fuse anymore. A rather happy accident lead to the discovery of a connection problem. The key was accidentally left on, and in the process of checking the rest of the fuses I jiggled the fuse box and heard a faint click from the relay that controls the fuel solenoid. That gave me the idea that there is a loose connection in the fuse box itself.
And, sure enough after bending the connections a bit in the fuse box, the relay stayed on and after I reconnected the solenoid, it also worked, and the no fuse blew. The tractor started up and ran like it always have.

Next, I opened a beer, that I happily drank while we put the machine back together. (I reconnected ALL of the safety switches too)
I drove the tractor home and parked it in my unheated garage. That night the temperature hit a balmy -13F. In the morning, after two hours of block heater it started right up and ran like the champ it has been for years.

To be honest, I am not certain if I did find the original problem, or it just went away in the process of moving the wires as I tested them with the multimeter.
The local dealer did give me the wiring diagram, that I used a lot. Coincidentally the wiring diagram for the B7800 was posted in a separate thread so I am including a link to that, in case some other poor bugger will need it in the future. Look for it in reply #16.

 

[sixdogs]

Problem solved and that's all that matters. Congratulations.
The B7800 is one heck of a fine tractor.

 

[Leejohn]

Where is the link? That reply #16 didn't get it.

 

[AWSubie]

How about this image?

 

[easygo]

Where is the link? That reply #16 didn't get it.

I will try it again. Hopefully this works.
http://www.tractorbynet.com/forums/...6-b7800-alternator-upgrade-2.html#post4953390

 

[Leejohn]

Got it, thanks.

 

[tysmobiletractor]

So, what was it?

 

[Henro]

So, what was it?

Read post #12