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I just purchased an old yellow deck JD STX38 in near perfect condition. The battery is probably not the best but a few days after charging it is able to start the tractor. When I tested voltage was at 13.6 while running. After about 20 minutes of mowing the battery is completely drained. How many amps should the clutch pull normally?

No more than 5 amps per minimum allow PTO resistance of 3 ohms per the service manual.

StarTech said:

No more than 5 amps per minimum allow PTO resistance of 3 ohms per the service manual.

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Thank you, does the manual say where to measure this?

I'd test the charging system and try again. If the charger is putting out 13.6 and the battery is still drained, something is wrong with that, whether it is the charging system, the diodes, connections or battery I can't say. Most lead acid batteries last a max of 4 - 5 years, and less if they are allowed to go flat and sulfate.

tooler said:

Thank you, does the manual say where to measure this?

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The resistance is measured at the PTO clutch. The reason to measure the resistance instead amp draw is most meters can't handle high current unless they are design to.

Also these PTO clutches can be partially shorted and still work. When they do they draw more current than charging system can provide they and drain the battery. I have seen PTO clutches to up to 20 amps and still work. Several years I had one customer to refuse to except his PTO clutch was bad even though it was melting the wiring insulation because it was still working.

Also note the charging system must be working properly in order recharge and provide for current demand. So it needs to be tested too.

Hi Tooler,

I happen to have one of these among my collection of riders. They have always been a popular model. I've never understood the dispute/preference between the "yellow deck" and the 'black deck models". Maybe it is a color scheme thing.

Disconnect the PTO clutch and measure the Ohms resistance between the 2 harness connector pins of the clutch. Let us know what the reading is.

You checked voltage after the battery just came off the charger, that is called "surface charge" and does not mean the battery is good. The old battery is still questionable. If this set for a long time, don't expect the battery to be any good. These small batteries are not as robust or reliable as a typical vehicle battery.

A meter can read voltage, but it cannot test or verify amperage. Voltage is potential to do work; Amperage is what gets the work done. This is where meters can trick a person. (Gives false hope)

I think your charging system is not working properly and that will cause the PTO clutch to pull down a battery pretty quick. The PTO quitting is a symptom, not a cause.

Get a new battery in this and then check the charging voltage while running at high RPM. It should show higher than battery voltage when tested at the battery. Usually, around 14.2-15V is what I look for.

If the voltage stays a battery voltage, you need to start looking at the charging system.

I will stop here for now.

We can also help you cover that problem as needed.

I just discovered that I am missing a module of some sort that should be bolted to the engine cowling just over the fuel shutoff on the Kohler Command 12.5hp. The wire that is supposed to plug onto it looks like a giant fuse holder. What am I missing?

A picture would be most helpful My imagination recall has the memory bank overloaded at the moment.

Wild guess is that the voltage regulator has been removed and forgotten about before you purchased the mower, or it was sold because the previous owner could not figure it out.

Auto Doc's said:

A picture would be most helpful My imagination recall has the memory bank overloaded at the moment.

Wild guess is that the voltage regulator has been removed and forgotten about before you purchased the mower, or it was sold because the previous owner could not figure it out.

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yes I just looked at the manual,it must be the rectifier/regulator. It is shown over the oil filter in top left picture.

At least whoever stole it left the screws in! are these things subject to failure? I will borrow one off another tractor tomorrow to try. https://www.amazon.ca/partszen-Volt...2da3b90a136dd33ca059c21&qid=1757119960&sr=8-6

They are not that failure prone unless it has been run with a dead/bad battery for a very long time. The charging system on these are only meant to maintain the battery and run the PTO clutch and lights as need. Thy are not meant to constantly recharge a bad battery.

If it mounts to the plastic cover, it will need a short ground wire run from an engine bolt to a regulator mounting bolt for it to work properly. The voltage regulator body must have a proper ground.

You will need to check for AC voltage from the 2-wire connector coming from the stator. It should show roughly 25V AC at high RPM unplugged from the regulator. If not, the stator has issues, or the flywheel magnets have come unglued and now sticking to the stator. (We'll cross one bridge at a time) Let us know what you find.

Teryl Fixes All has a good video and information about this flywheel charging magnet problem and how to correct it.