My 2007 MDX tail light don't work, but the brake lights do. Seems to use the same bulbs. It appears to be a led light but I can't can find a replacement from the local auto parts store.

 

Forgot to add this only affects the passenger side lights.

 

The 2007 have FULL LEDs Brake-lights so there is no bulb to be replaced in the housing for that (Reverse lights, Side-blinkers and Parking lights do use common Halogen Bulbs)… If the brake light does not work you have to get it diagnosed.

Turn Signal use 7440 bulb
Parking Light use 168 bulb
Reverse Light use 921 bulb

 

Smirmich, the brake lights do work, it's just that when I lift my foot off the brake pedal at night, those light go completely out.

 

The driving lights (Brake Lights Dimm) are the problem?

 

The brake light looks fine.

 

OK you need to understand that the LED Brake Lights are also the Driving Lights (They have 2 brightness settings).
When you turn on the driving lights the Brake Light should light up (At a dimm level this is know as the "driving light").
When you press on the brakes the "driving lights" goes full power then it becomes the Brake Lights.

Knowing that:
When you turn on your driving lights the brake lights do not turn on, on the dimm level? they only light up when you press the pedal?
Perhaps a PICTURE of your issue could be very useful here?