TD75D Starting Circuit

downslope · Nov 30, 2017

TD75 tractor had been acting up a little when turning key to crank position. At times had to hold and release a few times to get it to crank, now it won't crank at all, no click, nothing. Battery is charged and with key in run position horn and head lights work. PTO warning light turns on and off as it should when PTO lever is moved. There is +12 volts at the big terminal on the solenoid.

Is the small wire to the solenoid supposed to have +12 volts showing when key is moved to crank position?; it does not. Or does the key complete a ground path to the solenoid? At this point I suspect the key switch, or maybe a faulty safety switch. Is there a safety switch on the shuttle shifter to be in neutral? On the clutch pedal to be depressed?

Anyways, how do I access the backside of the ignition switch for testing/replacement if necessary? The nut securing the switch assembly to the dash panel was a little loose, this could be a problem if the key-switch is completing a ground to the solenoid, will tighten up tomorrow. What would I have to jump to the solenoid to determine if it's defective. Thanks for any/all advice.

TractorTech · Dec 3, 2017

Two of the items. The key sends 12v to the solenoid. You can apply 12v to solenoid terminal to bypass switches. MAKE SURE TRACTOR IS IN NEUTRAL.

downslope · Dec 6, 2017

TractorTech said:
Two of the items. The key sends 12v to the solenoid. You can apply 12v to solenoid terminal to bypass switches. MAKE SURE TRACTOR IS IN NEUTRAL.

Thank you for the info. I applied 12V to the solenoid and it cranked and started right up.

Now I have to figure out where the exact problem is with either the key switch, safeties or wiring. Do you know if the safety switches are in series between the ignition switch and the solenoid, or are they before key and interrupting 12V to just the start portion of the key switch?

Does anyone know how difficult it is to access the back side of the key switch on this model tractor (open station)?

TractorTech · Dec 6, 2017

downslope said:
Thank you for the info. I applied 12V to the solenoid and it cranked and started right up.

Now I have to figure out where the exact problem is with either the key switch, safeties or wiring. Do you know if the safety switches are in series between the ignition switch and the solenoid, or are they before key and interrupting 12V to just the start portion of the key switch?

Does anyone know how difficult it is to access the back side of the key switch on this model tractor (open station)?

Not real hard to get to switch by removing LH dash cowl panel, but I would check your safety switch on the PTO lever. It is located on the RH side under the deck and is activated by the PTO lever. The other switch would be on the clutch.

downslope · Dec 6, 2017

TractorTech said:
Not real hard to get to switch by removing LH dash cowl panel, but I would check your safety switch on the PTO lever. It is located on the RH side under the deck and is activated by the PTO lever. The other switch would be on the clutch.

The PTO lever on this tractor is on the left side, ie you operate with your left hand while sitting in the seat. The key is on the right, by your right hand. The reason I suspect the key switch is when the tractor was acting up intermittently you could get it started by jiggling the key a few times. The PTO lever does turn the PTO warning light on the dash on and off, but of course the contact that controls the starter solenoid may be bad.

Are the screws that hold the cowl panels covered by the floor mat? Thanks again for all your advice.

TractorTech · Dec 7, 2017

downslope said:
The PTO lever on this tractor is on the left side, ie you operate with your left hand while sitting in the seat. The key is on the right, by your right hand. The reason I suspect the key switch is when the tractor was acting up intermittently you could get it started by jiggling the key a few times. The PTO lever does turn the PTO warning light on the dash on and off, but of course the contact that controls the starter solenoid may be bad.

Are the screws that hold the cowl panels covered by the floor mat? Thanks again for all your advice.

Sorry for the dyslexic moment. Yes, I believe the cowl screws are under the lip of the floormat. I'm with you as to ignition being the culprit.