[MOTORHEAD]

Tom; If two lites per side work in the tail lites, try two per side in the front. As a test, you only need to try it on one side. Take both leds for the front, put one in the socket and "clip lead" the other one in parallel with with the first. If that doesnt work, use the incandecent bulb parallel with the LED and see what happens.
Think: WWED (What Would Edison Do ? )

Ted
ps; Your car doesn't have the big brake lite/tail lite relay, does it ?