[...]>I notice arstech also mentions powering, and I notice in the pinoutfor the ISA connector, there is a pin available for -5V. On modern ATX
power supplies, -5V has been removed, and you'd find one pin on
the ATX connector that is not being used. That would be where the
-5V used to be. Now, there isn't a strong reason to be using
that rail. It might be convenient for something like wiring up ECL
chips. Or perhaps some of the really old DRAM technologies. So that might
be an item to check as well.
Back in the day, the -5V was often used in UARTs. If the OP's custom cardis
*that* old and relies on serial communication devices that are not single,
positive input voltage, that could be a problem requiring resolution...
.... not too hard to provide the -5v from a regulated wallwart though,