TC40DA Blows #5 Fuse After 15-30 Minutes

[dakota52]

My New Holland TC 40 DA has started blowing the 7.5 amp number five fuse. This takes out my high speed range (rabbit/turtle switch) and cruise control. The tractor starts fine and will run 15-30 minutes before the fuse blows. I have looked for a frayed wire but haven't found any. I tried changing the high range shift relay and that hasn't helped. Can the diode be bad? I will appreciate anybody's suggestions. This is getting very frustrating. Up until now the tractor/cab had been fine.

 

[jinman]

The chance of a diode pack being bad is very slim. Much more likely is a faulty cruise control magnet under the right-side operators platform or the range solenoid on the left side of your transmission under the left operator's platform. Have you checked wiring there? The wires to the rabbit/turtle solenoid are very exposed.

If you are not using cruise, then the cruise magnet is likely NOT the problem. Fuse 5 also supplies alternator excitation voltage. Does your alternator seem to work okay? If there is a problem with the alternator, the light on the instrument panel should illuminate.

 

[dakota52]

The alternator seems to work fine and the dash light isn't on. It did it again this morning and I didn't even have cruise on. How do you access the wiring under the rabbit /turtle switch? Do I have to remove the right rear tire to gain access? I can't figure out how to get the panel off under the cruise switch and rabbit/turtle switch. Thanks for help and suggestions.

 

[jinman]

There are bolts for the right side panel under the fender and you do not have to remove the tire to get to them. Also, there is a connector for the joystick rabbit/turtle switch under the rubber boot of your joystick.

Does the fuse blow only when you are in rabbit? The solenoid for the speed control is under the left operator's platform and is energized only when you shift to rabbit speed. If the fuse blows in rabbit, but not in turtle, then the problem points to the solenoid or its wiring. The diodes for rabbit/turtle only function to aid switching. If you can switch from rabbit to turtle and back, then the diodes are good. I think you have a wire rubbing or chewed by a critter somewhere.

 

[dakota52]

I am heading out to the shed to check both the wiring again and the range solenoid. I will let you know what we find. Thanks so much. This is a frustrating problem.

 

[dakota52]

I checked the wiring near my range solenoid and didn't find any breaks in the insulation. I had to reconnect the wires to the solenoid a few years back and at that point I covered them with wire loom to protect them. I pulled the solenoid coil and put it on a battery for about an hour to see if the resistance changed. The resistance started out at 10.0 ohms and was 14.2 ohms after an hour. So it doesn't look like the solenoid is heating up and drawing too much current.

My plan tomorrow is to run the tractor in cruise without the coil installed and see if the fuse blows. If it doesn't, then I will flip the rabbit/turtle switch to rabbit and see if I can run for more than 30 minutes without blowing the fuse. I will also check the wires to the alternator and see if I find anything there. Hopefully something will show up. Thanks again for the help.

 

[dakota52]

I ran the tractor the other day without the range solenoid coil installed to see if I still blew fuse #5. What I found was that without the coil installed I still blew the fuse about 30 minutes (consistent with what I have been seeing) after pushing the rabbit/turtle switch to rabbit. If I left the switch in turtle I never blew the fuse. I also tried running my cruise control and never blew the fuse with cruise on as long as I stayed in turtle. Because there is a consistent amount of time between fuses blowing I think a part is getting hot with time and drawing too many amps blowing the fuse. At least I now know it isn't the range solenoid which is a pricey part!

I re-checked all the wiring from the #5 fuse to the range solenoid and to the rabbit/turtle switch on the fender today. Thank you to jinman for the advice on how to access the fender rabbit/turtle switch. I also checked the wires to the alternator. I didn't find any breaks in the wires. I didn't remove the black braided protector from the harness and hope that my problem doesn't lie with a wire rubbing inside there.

I am starting to wonder if my rabbit/turtle switch is causing my problem. Does anyone know how to test the switch? Could it be heating up when in rabbit mode and the drawing too many amps causing the #5 fuse to blow? I noticed when I removed the switch that there were a lot of wires connected to it. I expected a SPDT toggle switch with 3 wires (common +12V, rabbit, turtle) so I am confused about what the extra wires are doing. I appreciate any help that is offered. At least I can use the tractor in turtle mode for now.

 

[jinman]

A while back, I posted the details of how the Rabbit/Turtle circuit works in this thread. I should have sent you to the thread before, but didn't think of it until now. With your detailed info in your last post, I think we can make some analysis and eliminate a couple of things.

You said you replaced the hi-shift relay. That leaves the low-shift relay, but all it does is provide ground for the high-shift relay coil. If it were grounding out, the circuit would not care since its function is to provide ground anyhow. With that info and your troubleshooting, all that's left is the diode pack, switches, and wiring. You can eliminate the joystick switch by disconnecting it and using only the fender switch. The contacts of the fender switch are open after you set Rabbit, but power comes to the light bulb for Rabbit.

The same power that holds the range solenoid powered is fed through the latch diode to hold the hi-shift relay coil energized. It's ground path is through the low-shift relay contacts to ground (see slide #3 in the linked thread, 1st post). The diodes are in the same general location as the relays under the cowling on the left side below the steering wheel. A diode pack contains both diodes. If one of those is heating up and shorting to ground, it could cause the problem because the diode is before the hi-shift coil and that would pop the fuse.

I know you wondered about this diode pack in the beginning and I played it down, but I think you should probably go ahead and replace it based on your excellent troubleshooting. You just can't troubleshoot something that works for 30 minutes and then shorts out internally unless you feel the heat or see burn marks or smell odor. I know it's a bit of an Easter egg hunt, but if your wiring is all good and not mouse chewed, I think changing that diode pack is the next move.

 

[dakota52]

jinman,
Thanks yet again for the response and help. I don't want to sound like I am questioning you, since you are definitely an expert on tractor electronics, but can you please double check something for me. I am not sure that the diode pack can short to ground. I reviewed the wiring diagram in my owner's manual and only see hot (12V) wires going to/from the diode pack and no grounds. Without a ground somewhere in the pack I don't think it could short internally. I may be missing something here so if you would please check this for me I would appreciate it. I can send a copy of my wiring diagram if you need it.

I now understand all the wires for the rabbit/turtle switch. The extra ones are for the lights that turn on to indicate which speed is active. Everything looks good on that switch since the lights activate correctly so I don't think the switch is shorting and blowing the fuse. I don't have a FEL or joystick (should have mentioned that earlier) so I don't have to worry about that.

When I looked deeper into the wiring diagram I noticed that fuse #5 also powers the park brake relay coil. I think I will try swapping this relay with a different one and see what happens. I also noticed that fuse #5 powers a wire going to the instrument panel that is labeled "SW B+". I assume this means "switched battery positive"? I am not sure how the instrument panel routes this power so there may be additional circuits coming out of the instrument panel that I haven't considered that are also powered by fuse #5. I may have to pull the instrument panel and see if I can tell how everything connects if I don't find my problem elsewhere. Thanks in advance for any help that is offered.

 

[jinman]

You are correct. The one and only way the diode pack could be blowing the fuse is if it's shorted to the case and that's grounded through the mounting screw or the case is grounded. It could also be the socket. I believe from the parts diagram that the diode modules are plugged into a socket like relays. The real point I'm trying to make is that to blow the fuse, it has to be a short to ground before any relay coil. Since you replaced the hi-shift relay, there is no way the lo-shift relay can cause the problem. Of course, there is the high shift relay's socket. . . see what I mean?

Trying to troubleshoot through a forum has lots of problems. I'm a hands-on guy in a decidedly hands-off environment. That said, didn't you just post that no fuse blew if you just left the transmission in turtle? If so, it would seem a bit off target to go looking for other sources of a short. Surely if there is no fuse blown in turtle, it is related to something in the hi-shift circuit. Does that make sense?