but how would I tell whether I've connected them upside down?

Usually at least first pin is numerically marked on PCB.

The Serpent Rider wrote on 2021-01-08, 13:21:

but how would I tell whether I've connected them upside down?

Usually at least first pin is numerically marked on PCB.

They're not as far as I can see. The pins are only marked with the port that they support, but there's no additional information.

EDIT:

I finally figured it out. Apparently the jumpers have missing wires that line up with missing pins in the pin headers, indicating how the jumpers should be attached.

I realized just now that I missed this because my motherboard's layout differs from the manual, so I was looking at the wrong pin headers.

The one thing I still can't figure out is where the serial port's jumper goes?

There's no jumper, you set it in the bios if you mean for com1/com3 com2/com4

evasive wrote on 2021-01-08, 20:13:

There's no jumper, you set it in the bios if you mean for com1/com3 com2/com4

I'm sorry, I'm not sure I understand your comment.

I'm trying to ask where on the motherboard that I'm supposed to plug in the serial port's jumper, and how to make sure that I'm not plugging it in upside-down.

can you take a decent photo of the pin outs on the mother board and post them. Cant tell anything by that schematic other than where pin 1 is. Becasue I am kinda skeptical that you have the wrong usb connector and you need to make custom ones. The PS2 connector is fine, but I am not sure the pin out is right.

But you need to do some photos and more work if you want my help.

Warlord wrote on 2021-01-08, 20:39:

can you take a decent photo of the pin outs on the mother board and post them. Cant tell anything by that schematic other than where pin 1 is. Becasue I am kinda skeptical that you have the wrong usb connector and you need to make custom ones. The PS2 connector is fine, but I am not sure the pin out is right.

But you need to do some photos and more work if you want my help.

It's not the USB connector that I'm trying to connect anymore (since I managed to figure that out) - it's the serial (RS-232) port that you can see in image #3.

I'm just trying to figure out what kind of pin that it's supposed to connect to.

EDIT:

I found out that the serial connects to the COM ports, and that the ribbon cable's red side should be aligned with the same side as the "pin 1"-pin - which as I understand it can usually be identified with a "1" written- or a white box or arrow drawn on the board next to the correct pin on the pin header.

So I suppose that's all my questions answered. Thanks so much to everyone who took the time to answer!

Good job and glad you figured it out. Sorry late to the party, had to work late. Suggest next time if you give the actual board make and model it would help as many of us have pinouts for various boards.