LED tails installed, now lights don't work!

[Rhino]

diodes HAVE to be wired to the correct polarity, as opposed to an actual bulb which can go either way.....do you have 12v to the brown wire?

Absolutely correct. A diode (which includes the LED) is a one way street for electricity. From the OP's post I would agree that it's wired backwards.

I hooked up black to brown and red to yellow/green, now my tails do not work. Front lights work fine. Ideas? Thanks!

If you're positive the polarity is correct, have you measured the voltage between the positive wire and the ground you're using?