If you look closely at the PCB labelling where the front panel headers are on the motherboard, you should be able to see which pins are +ve/-ve. Can you pass on an image for us to see that location? You will need to host your images on Imgur or their ilk and then pass on a link for us to see.
Yes that is what I was looking for, if you transplant the labeling on the PCB onto the pins, you get the terminal polarities. You can use this video as a guide;