Tractor Manuals???

Steven, the short answer is the charging system is not working properly or the PTO clutch may be going bad and drawing more current than the system can supply. If I remember correctly the STX38 has a 12.5 or 13HP Kohler Command engine, which has an electronic ignition that operates like a magneto. The engine only needs the battery to run the starter motor. Ignition is supplied by the flywheel magnets and the electronic module/coil. Could also be as simple as burned, rusty, or corroded wiring connections not getting charging voltage back to the battery.
If you have a volt/ohm meter and know how to use it, we can walk you through some tests to narrow down the problem. The tests will be best explained in the service manual for the tractor. If you don't have a JD service manual you can download info for the engine and it's electrical tests from www.kohlerengines.com. There won't be any info for the clutch since it is a "tractor part".
Let us know how it's going.

tommyhawk

I don't have the specs. for that clutch, but most of them work best in the 3.5-4.0 ohm range. If you have an ohm meter, just plug each probe into the connector, doesn't matter which goes where. If the reading is way off, we should try to find the exact reading for the clutch you have.
Does yours have a "MAG" brand or a "WARNER" brand clutch? Most Warner brand are adjustable and the coil can be replaced if bad. The MAG brand clutches I've seen are not designed to be taken apart.
If you don't have a meter, I'd bet you have a friend who does.

tommyhawk