TC40D Hi/Lo speed shift blows fuse

[PlanterDude]

My tractor is running fine in the default Lo speed. If you replace the 7.5 amp fuse the switch will light up but as soon as you try the Hi speed either on the fender switch or the FEL control stick the fuse blows. Anyone know how to test the switch or the shift solenoid on the trans? Thanks for your help. Life's too short to be stuck on turtle!

 

[jinman]

To check the solenoid, remove both wires from the connectors and measure the resistance of the coil. It should be 7.5 to 10 ohms. That means it normally pulls 1.4 to 1.8 amps. You also have a couple of relays (Hi-shift and Lo-shift), and a diode logic pack in addition to the solenoid. I would also check the Rabbit light on the fender switch. If it is shorted in the socket, that could also pop a fuse when you shift to Rabbit.

Got to this link to read a full description of how the circuit works with simplified diagrams showing operation.

 

[PlanterDude]

To check the solenoid, remove both wires from the connectors and measure the resistance of the coil. It should be 7.5 to 10 ohms. That means it normally pulls 1.4 to 1.8 amps. You also have a couple of relays (Hi-shift and Lo-shift), and a diode logic pack in addition to the solenoid. I would also check the Rabbit light on the fender switch. If it is shorted in the socket, that could also pop a fuse when you shift to Rabbit.

Got to this link to read a full description of how the circuit works with simplified diagrams showing operation.

Thanks for Ur fast response Jinman. The solenoid reads 11.8 ohms, a little high but not enough to blow a 7.5 amp fuse.

I am sure there is a short somewhere. I have checked the rabbit and turtle relays, even swapped with the cruise one and they are all fine. I checked the switch on the FEL stick and it is working right, no shorts there. I noticed that when the fender switch is in the circuit whether there is a fuse or not I read a short to ground on the purple wire at the solenoid. The black wire is of course a ground. I know the solenoid works since I applied 12v to it and it cycled.

I removed the fender switch and ran the tractor, when switching to rabbit on the FEL stick the fuse blew. I then checked continuity at the leads to the solenoid again and black to ground had continuity and purple to ground showed no continuity which I thought meant the hi speed relay was OK for sure.

My thought is that the fender switch may be good and just allowing a short to show up when it is in the circuit and that the short may be in the latching diode or in wiring to or from it. Can you tell me where to look for it? Your thoughts too, please.

Also I know that during checking with a good fuse both lights work, turtle is steady but rabbit is momentarily until the fuse blows when shifting to rabbit.

 

[jinman]

Although I don't see how the diodes could cause the fuse to blow, they are located under the black cowling below the steering wheel on the left-had side. There's a board there with the relays. There are 6 small relays and to the left of them there are two modules. The top one is for the cruise control and the lower one for the Hi/Lo speed control. I would just swap them to see if the problem goes to the cruise control magnet circuit.

There is a possibility that something else that uses fuse #5 is drawing more than normal current. When you engage Hi speed, it could be the 'straw that broke the camel's back' so to speak. Have you checked operation of the cruise control to make sure it doesn't blow the fuse also? I'm still thinking there might be something wrong with your fender switch. I would disconnect it and use the joystick switch to go to Hi/Lo. They are just in parallel, so you can disconnect the fender switch and the joystick should still work fine.

Also, fuse #5 provides excitation to the Alternator. When you turn the key on but before starting the engine, you should see the Alternator light on the dash. That will tell you that the circuit is complete. When you start the engine, the alternator puts 12 volts on both sides of the light so there is no current across it and it goes out. If your alternator light stays on all the time, you could have a problem inside the alternator.

That's about all the extra info I can give you without putting hands-on. Do you have an Operator's Manual? There is a nice electrical diagram in that manual. Frames 5 and 6 show the circuits powered by fuse #5. Frame #7 shows the switches on the joystick and fender.

 

[PlanterDude]

Jinman, again thanks for your response. Just got back in after finding the short. Figured out which were the diodes by tracing wires at back of relay block. Once I determined there was no problem there, started taking her apart. First took off the right fender cover and then the seat so I could the follow wires under the deck through the openings. Sure enough the harness had rubbed through on a sharp edge. A few wraps with black electrical tape fixed that and I was off and running, that is, after I put the whole thing back together again and added a new fuse.

This experience has given me a very close and intimate knowledge of my tractor and all of its functions and subsystems.

Thank you very much for all of your help and especially the schematics! They were invaluable. CNH keeps service info on their tractors a tightly held secret ($300-$500). This forum is invaluable for folks who want to fix it themselves or in my case have the nearest dealer 1 1/2 hours away, a very expensive proposition whether you take it in or have them field service the unit.

As a side note I noticed on these forums a lot of instances of flashers and turn signals not working. I had the same problem also and wanted to share my fixes. First thing I did was get the left side cowling off after I checked the bulbs. I figured there had to be a Dot552 or similar providing the blink. I was right, it was mounted on the relay block next to the Naso control unit. I replaced it and got the flashers working, but still no turn signals.

I traced the turn signal problem to the switch, took it out and opened it up, cleaned the corrosion inside and voila had turn signals too!

I then advanced to the fun part (the short), again thanks for all of your help. I be a rabbit now!

 

[jinman]

Excellent! Now go catch that turtle before he crosses the finish line ahead of you.

 

[RonKane]

Excellent! Now go catch that turtl, e before he crosses the finish line ahead of you.

Hi Jim,
You are a gem of a person! I have read your posts, and your answers are so well thought out. Thank you.
My fender range switch is lit, but when I push it to hi it stays on lo. The fel stick does not work either. My tractor is a tc45da and runs only in the lo range. How can I trace wires that are mostly hidden .Also, can i manually switch the trtransmission into hi?
Thank you in advance.
Ron

 

[mahills]

Hello Everyone. I'm new to the forum, but have a similar issue. I inherited a TC40DA with a farm I purchased just over a year ago. The tractor had significant neglect and abuse but I was able to work through most issues and have it running great. After months of tracking down a high/low challenge I found part of the solution here in this forum. Big THANK YOU.. My fuse was blown. The local dealer's (service manager) only solution was to replace the instrument panel (called it a computer). Thankfully I did not fall for the $7xx+ solution, especially since that was not the problem. Now all the lights and switches are working as expected, but there is no shifting. Could the shift solenoids be stuck or sticking? Is there an easy way to test them without tearing into the transmission?

 

[Cowboypreacher]

where was the fuse located?
Never mind, I found them!

 

[mahills]

The fuse block is located under the instrument panel. You have to unscrew the panel, and all fuses are lined up directly underneath. Best of luck.