450d front panel cables help

So i was going to plug the cables of my 450d to the motherboard, but i noticed that they are not marked. For example the motherboard have clearly marked pins 'HDD LED +, HDD LED -' but the cable doesn't have anything so i don't know which way to plug it in.



The cable looks like this:

http://i.imgur.com/SsJ8F2L.jpg



There is an arrow on one side, but i don't know what it means.



Help.