tn75a wont shut off

   / tn75a wont shut off #1  

wholesale trans

New member
Joined
Mar 14, 2018
Messages
7
Location
lancaster ny
Tractor
tc35 tn75a
i have a tn75a when you shut the key off 1.3 volts remains on 7 different fuses and the tractor will not shut off. if i take a power probe and ground any of those fuses all voltage goes away and tractor will shut off or if i turn lights on with key off same result. i tried a new holland alternator thinking i might have ripple voltage but same result. i have pulled the instrument cluster looking for a wire rubbed but would assume it would have battery volts if that was the case.is it possible the fuel shut off solenoid could store the voltage after key is turned off.if i unplug fuel shutoff solenoid tractor turns off or if i ground it with key off.thank you in advance for any help or advice.
 
   / tn75a wont shut off #2  
not familiar with your exact tractor, but it could possibly be the key switch itself. you would need to ohm out the switch and see if its not killing the power.
 
   / tn75a wont shut off
  • Thread Starter
#3  
thanks for the idea i just went and tested the ignition switch it checked out good . i even unplugged every wire with the tractor running and the key in the off position still have 1.3 volts. if i unplug the instrument cluster the tractor will shut off does anyone know if there are any capaciters in the cluster
 
   / tn75a wont shut off #4  
Do you have a wiring diagram for the tractor? IMO, that would be where to start. In the meantime you can verify 'stray voltage' by removing ignition key, disconnecting the negative battery cable and between it's end and the negative battery post, place a VOM set on highest AMP scale and see what it reads. This test could give clues to what is going on.

While doing the above test look for any corrosion, loose cable connections, etc. that might be present. What year tractor, #hours on clock, etc?

Also, since grounding various things, including the shut-off solenoid seems to allow for shut off, I'd take a good jumper cable and use it to a clean frame metal in place of the OEM cable to see if it allows for all circuits completion to ground when you go to shut off the tractor. Often the negative cable, and sometimes the positive one fail beneath the plastic sheathing and don't allow for adequate grounding...
Report back results....
 
   / tn75a wont shut off
  • Thread Starter
#5  
Do you have a wiring diagram for the tractor? IMO, that would be where to start. In the meantime you can verify 'stray voltage' by removing ignition key, disconnecting the negative battery cable and between it's end and the negative battery post, place a VOM set on highest AMP scale and see what it reads. This test could give clues to what is going on.

While doing the above test look for any corrosion, loose cable connections, etc. that might be present. What year tractor, #hours on clock, etc?

Also, since grounding various things, including the shut-off solenoid seems to allow for shut off, I'd take a good jumper cable and use it to a clean frame metal in place of the OEM cable to see if it allows for all circuits completion to ground when you go to shut off the tractor. Often the negative cable, and sometimes the positive one fail beneath the plastic sheathing and don't allow for adequate grounding...
Report back results....

Thanks for your reply all good ideas unfortunately I had already done that my fault for not posting that.i have less than .1 of a volt on the positive and ground side when performing voltage drop tests I also cleaned all the grounds and did supply more grounds through jumper cables. I do have the factory manual and have been looking at wiring diagrams . It acts like when you have a corroded connector and voltage back feeds through the circuit . I did find mouse **** behind the instrument cluster but couldn't find any chewed wires but I'm gonna pull the whole wiring harness out and take a look . Btw it's a 2006 with 853 hours thanks for all the responses so far
 
   / tn75a wont shut off #6  
This is a tough one. I don't know if yours is like my td80 but I have no idea what the device bolted to the alternator does but, it looks like some sort of device to dump errant voltage to ground since it's tied to the alternator. If that device has a diode in it it could be the source of your voltage leak. An easy way to check would be to unbolt it from the alternator. Just taking a WAG at it.
 
   / tn75a wont shut off #7  
OP's first post:..."i tried a new holland alternator thinking i might have ripple voltage but same result."

To the OP - Mice sounds like a good track to follow- they can and will do serious damage to wiring- given the chance to.
I'd look closer at the shut off solenoid and it's wiring schematic. Assuming it's NO and closes on contact when the key is turned to OFF, it could be sticking or just worn out and not closing fully, thus allowing fuel to still flow and keep the tractor running...You're test of adding a ground to it could indicate it is internally whipped, (technical term), bad windings/contacts etc. It does shut off the fuel supply when you add a ground. Can it be dismantled enough to see what's inside? Remove it's cover?
 
   / tn75a wont shut off #8  
IIRC, there are normally two coils in these solenoids. On is for the pull in (high current) and the other is for the hold in (low current). The pull in is on a timer and it 's only on when the Key is in the "Start" position and a little while after and the other one is on when the key switch is in the "Run" position. Putting the key in the "Off" position de-energizes both circuits. If you have some voltage at the solenoid with the key in the "Off" position, I'd suspect something in the Start circuit to the pull in solenoid.
 
   / tn75a wont shut off #9  
with the tractor running if you pulled the fuel solenoid wire terminal off the fuel solenoid shouldnt that kill the engine?
 
   / tn75a wont shut off #10  
Yes KY it SHOULD.. but in post #1 he says it does..
If you google>> "tn75a shut off solenoid" theres a utube video of a guy diagnosing a shut off problem..
 
 
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