Straight wired but is fused at 5 amps. Nothing has changed as far as wiring since
Voltage is lower than it should be when clutch is energized. (and you say it's direct wired to the battery) if so the wiring is too small or bad connections.
If the 5 amp fuse never opens/blows and it has a melt down, it's due to clutch FRICTION being to high for some reason such as low voltage plus friction load too high due to bad deck or otherwise
Might try letting the deck run for awhile, then kill the engine and use your IR gun and check the temp of the temp of the deck bearings, make sure deck blade brakes are working properly check the temp of the all you can after it's run for awhile.
If it's not overheating without mowing then mow for awhile and check temps again. If the clutch itself is slipping due to low voltage it will overheat fast.
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