4720 keeps blowing ignition fuse

[Karl2]

This is a follow-up to this thread here:

http://www.tractorbynet.com/forums/john-deere-owning-operating/142452-4720-wont-crank-both-power-2.html

Now that I have pinned down the issue as an ignition problem rather than PTO safety switch failure or computer glitch I thought it would be simpler to start a new thread to address this more common problem. Members should only read the other thread if they enjoy reading about somewhat clueless and slightly tedious troubleshooting sequences that lead to the pinpointing of a specific problem.

Simply put, my ignition fuse keeps blowing every time I attempt to start the engine. Yesterday I had been using the tractor for about 4-5 minutes when it suddenly died and would not crank, not even a click, even though everything else worked. Symptoms were the same as attempting to start with PTO engaged, but the PTO was not engaged. After many hours of troubleshooting I finally noticed that the ignition fuse keeps blowing when I attempt to start the engine. What would be the most common cause of this?

If it's of any help it was unseasonably hot up here yesterday, about 85 degrees and the tractor sits outside in the sun all day. I've only used this tractor in wintertime before so I'm not familiar with heat related issues that may affect it. I used AC in the cab but at a low blower setting, I would say cab temp before I used the tractor was at least 100 degrees. Could this affect wiring?

 

[Karl2]

Jeez this is getting frustrating, I know I can fix this with some patience and caution but my immediate problem is to simply get the tractor off my driveway's end and back near the house where I can more effectively work on it.

I parked the tractor in such a way that it blocks entrance to the driveway, not too brilliant but I wasn't expecting it to die on me there. Now my wife's car is parked on the side of the road and I can't get my pickup truck out of the driveway, the presence of deep ditches forbids driving around the tractor. We tried pulling the tractor with my truck (a 4x4 F150) but the driveway is a slight grade and gravel, so that was a no-go. All 4 wheels on the truck were skidding and the tractor actually pulled the truck back about 10 inches when I released the park brake with the wife driving the truck. Never realized until now just how heavy this "compact" tractor really is! Only way the truck can pull it is when it's loaded on a trailer and even then, truck balks.

Standard tow would not touch it, I was told I needed a heavy-lift tow and since we live in the middle of nowhere (or so the tow guy said) they want to charge me $700 for a 600-foot tow (length of the driveway), no friggin' way I'm paying that. Nearest JD dealer is 3 hours away and I know by experience a service call will run me even more. I don't think this fuse thing is a serious issue and I'm pretty confident I can fix it, but not where it's sitting now.

Since this is a diesel I am now seriously toying with the idea of bypassing the ignition to get the engine going long enough for me to drive it back to the house. I know it can be done, just not too sure what exactly has to be done to juice up the starter motor, I suspect it involves screwdrivers and sparks as I recall my late Grandpa doing this routinely with his tractors and dozers.

 

[Karl2]

Hmmm... not that much info on the Net on how to bypass-start this type of starter, but plenty of info about the dangers of bypass-starting tractors that are in gear and explanations on why modern tractors have a seat switch that prevents starting while not in seat.

I am aware of the hazards but but my tractor is hydro and JD is confident enough that hydro tractors won't run the operator over that they let us start them even when we're standing alongside the tractor and obviously not in seat, something I do routinely in winter when I want to warm up the cab without having to sit on a cold seat. Apparently other types of tractors won't let you do that and for good reason, judging from the multitude of accident reports I stumbled upon that involved operators bypass-starting tractors that had been left in gear. I understand some people abuse bypass-starting on problematic machines instead of fixing them, not a good idea.

I don't think it's possible for a hydro tractor to run someone over after bypass-starting it unless it's on a grade in neutral with park brake not engaged, in which case it can run you over even without engine running anyway. But to play it safe I nonetheless intend to bypass start my tractor with shifter in neutral and park brake locked to avoid unpleasant surprises. Don't really have a choice with the park brake anyway, if I disengage it while in neutral the tractor will roll down the slight grade and sit in the middle of the main road. To avoid any risk of accident the park brake's been locked since yesterday, chocks wedged underneath the wheels and shifter in A position.

 

[mfreund]

You should be able to pull the tractor in neutral. If not that is one steep drive or traction is bad.

You need a service manual for the tractor to effectively find out what is on that circuit. I know, if only!! I would pull the glow plug relay and see if the fuse blows. It is imposible to know what is on the circuit,but something has a dead short to ground. I wish I had a manual to help!!

 

[jenkinsph]

Karl you have my sympathy for what is is worth


You may have to weight the truck down to get the tractor towed back up the
driveway, I would do that first. You may find the tractor is easer to move if the range selector is disengaged by moving it between b and c positions.

If you know how to use a vom meter you may find the problem.

One question I have is does it blow the fuse if the ignition is in the run position or the starter position?
Much simpler problem if the start position only.



Steve

 

[jd110]

These tractors require more than cranking the engine to start. There is also afuel solenoid to energize. That will get the engine running. But it still wont move unless you power up the E-hydro computer. A better solution would be to tow or drift the tractor to a better location. If you put the range lever in neutral and release the brake, I would think your truck could tow it somewhere out of your way. There are several components pwered by your blown fuse. Among them are, Seat switch, instrument panel mode switch, fuel gauge, park brake switch, rear pto switch, mfwd switch, mid pto switch, and air filter restriction switch. Since it quit after you got off the tractor, I would start with the seat switch and park brake switch areas since these switches cycled when you got out of the seat and applied the brake. Try unplugging one of these components at a time until the fuse no longer blows.

 

[Karl2]

Karl you have my sympathy for what is is worth


You may have to weight the truck down to get the tractor towed back up the
driveway, I would do that first. You may find the tractor is easer to move if the range selector is disengaged by moving it between b and c positions.

Loaded the bed as much as I could, however that truck experienced transmission issues a few months back so I don't want to push my luck. Will try with selector disengaged tomorrow though, God bless the home office I won't be needing to go out and fortunately my wife can still use her car to go to work as it's not trapped.

If you know how to use a vom meter you may find the problem

Can do.

One question I have is does it blow the fuse if the ignition is in the run position or the starter position?

Starter position only

In the run position all the usual bell and whistles work as usual. In fact I tested every single electrical device (lots of those in a cab I noticed) and all work fine, battery power delivery appears to be in perfect shape. Tested all fuses by rotating them through the sockets of matching amperage and operating equipment hooked to the corresponding circuits, all worked fine except those plugged in F5 (ignition 15A) which kept blowing when the key was turned all the way to the right (starter position).

I also tested the 4 main relays, which are all of same value, by removing them and connecting each one in turn to the K4 relay socket (rear work light circuit) and turning on said light, which won't work if a faulty relay is used (I think). In any case it wouldn't work when there was no relay in the socket and worked fine with any of the four relays plugged in.

 

[Karl2]

These tractors require more than cranking the engine to start. There is also afuel solenoid to energize. That will get the engine running. But it still wont move unless you power up the E-hydro computer. A better solution would be to tow or drift the tractor to a better location. If you put the range lever in neutral and release the brake, I would think your truck could tow it somewhere out of your way. There are several components pwered by your blown fuse. Among them are, Seat switch, instrument panel mode switch, fuel gauge, park brake switch, rear pto switch, mfwd switch, mid pto switch, and air filter restriction switch. Since it quit after you got off the tractor, I would start with the seat switch and park brake switch areas since these switches cycled when you got out of the seat and applied the brake. Try unplugging one of these components at a time until the fuse no longer blows.

You may be on to something, prior to driving down to the main road I had played with the seat adjustment compressor until it bottomed out, maybe this damaged the seat switch and caused a short. I guess I can test this possibility by disconnecting the seat switch from the harness behind the seat, shorting the connector, and attempting to start? If the seat switch is faulty and causing the problem then bypassing it should get rid of the issue I suppose.

If that doesn't work, ideally I would proceed by bypassing every switch hooked to that circuit one after the other in order to eliminate each one as the source of the problem until the only switch left is the ignition switch itself? Do the switches you mention constitute the full list of switches on the F5 circuit?

So even if I managed to bypass-start the engine I still wouldn't be able to move the tractor? Wouldn't leaving the key in the "run" position allow computers and controllers to be powered?

 

[jenkinsph]

Karl,
If the fuse only blows in the start position then disconnect and separate the leads to the starter solenoid. Then turn the key to see if the fuse still blows, if it does not then you likely have a bad solenoid, if it does blow you have a
problem in the dash or wiring from start terminal to the solenoid. I don't have my manual yet for my tractor so I can't tell if the safety switches are in series with the starter circuit.

Another thing you may try is if the fuses don't blow in the on position then with the starter lead removed from the solenoid you may be able to start the tractor if you hot wire it.

Since most of these safety devices will stop the tractor while running I would expect them to be upstream in series with the ignition circuit. Placing them upstream means they can prevent starting as well as stopping the engine. The seat switch will diengage the ehydro but doesn't necessarily stop the engine.

My hunch is you have a short between the ignition switch start terminal and or the solenoid switch.



Steve

 

[Karl2]

By starter solenoid are you referring to the fuel shutoff solenoid? If there's a starter solenoid it must be built into the Bosch-made starter which may explain why it's not listed on the JD parts list...

But I can still test the starter motor by disconnecting it and see if the fuse still blows, can I? I doubt the starter would be at fault by who knows.