Well generally your Anode is your "longer" terminal of your LED also the positive.
Also from your drawing I would assume that it is anode->cathode because a typical diode symbol is --|>|--
It's a surface mount LED meaning that it doesn't have prongs as terminals.
And yeah, I did do a test with a voltmeter, and found out that I did have them on backwards.
But I still have a problem...
I changed a few around to the correct way that they should be mounted, and went back and tested it in my car expecting to see only those few light up.
Wrong. None of them are lighting up still.
I wonder if it's because they are all along the same circuit, and they have to all have the same polarity, or perhaps it's because at the bottom of the board, I'm missing two LED's due to the fact that on the board on one side, one of the mounting pads is missing, so I just left out the LED on that side, along with the LED on the other side so it would look like it's supposed to be that way.
Anyone know if this is perhaps why none of them are lighting up? Because two LEDs are missing?