I concur with RBR... the red striped side of the cable is supposed to point towards the power connector, inserting the ribbon & plug in the opposite polarity will make the FDD light come on and stays on during POST, also configure the BIOS/CMOS to seek the FDD & enable swap floppy disk drives (this will help it seek them despite them being on the primary OR secondary plug)
BTW I've had a motherboard overvolt and kill FDDs before (early pentium/K62 era) so it would be equally possible for a FDD onboard controller OR the drive itself to fail, did you check out the FDD on any other system?
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