I have no experience with this particular motherboard, but check if you have continuity to GND at pin 5 of your D-sub connector. If not, means that your bracket isn't the right type for your mobo.

Thank you!
I just checked and it looks like I do NOT have ground continuity using this bracket. I went ahead and checked pin5 of the header against ground, and that pin DOES have continuity, as shown here. So I think this would indicate my board has the normal style header pinout, whereas the bracket\connector I have is the old style?

Man, I suspect a new bracket will be loads easier and cheaper than a new IO card! Thank you for your help Quicknick! 😀

Edit: Also, since I have a spare bracket now that is apparently a non-standard, is there a place I can post it up for someone else to grab if they are in need of one?

Excellent! I realized I could remove the black plastic shrouding from the ribbon cable connection to the RS232 plug, and realized I could simply re-solder the connector in the correct method! Booted up the PC to windows 95 and it's alive! IT'S ALIVE! Feels great, like I've just conquered the universe! And I didn't have to buy anything to do it!

Thanks again so much for pointing me down the right path! 😁

There seem to be two prominent serial cable wirings found on computers os this general era. Best to keep a few of each around for testing. As a very general rule, it appears as is SiS 496 boards often use the same standard while UMC 8881 boards use another. I find this odd because the RS232 chip is not part of the chipset.

I have seen two sort of wiring :

11 3 5 7 9
2 2 4 6 8

(used on all my machines newer than pentium1)

11 2 3 4 5
2 6 7 8 9 

(used on some of my pentiums and on all my older machines)

You can see which one is it by unscrewing the connector and sliding back the plastic.
First one has staggered cables where every other wire goes to the other row.
Second has a split in middle of the cable with one going to top row and other going to bottom row.