Thanks for the links there : D

I'm guessing I need to replace the bulbs, but maybe the wiring is shoddy, because the spoiler brake light doesn't work either.

you might have to replace your tailight failure box. its right in front of your drivers tailight behind the panel. its about 2" x 2" x 1". i think yours is yellow because its an N/A. mine was but then i put the spoiler on and had to change to the white one so that it would send the correct voltage to the spoiler to light up the led. yours maybe be white though b/c you have more options on yours than i have

Really? I already pulled it and opened it up and everything looked fine. It's yellow. My dash doesn't even show that some of my tail lights are messed up (even though that's what the box is supposed to do). Maybe it just crapped out, even though I can't see any burn marks or shoddy soldering.

I may be wrong, but didn't the spoiler only come on Turbo models? My 87 N/A has almost all of the options and it never had a spoiler...

I have a third brake light in the window, so maybe whoever put the spoiler on there (if it's not a stock piece on any N/A's) didn't switch out the box. Also, the Yellow box I believe is for the pre-89 supras and white is for the post-89 models. If you have a 3-piece spoiler than you should have the white box (if what I stated is true; someone please correct me if I'm wrong).

Also, if you have the 89+ lights (with the red piece in the middle) you would also need the white box.

Well, it's a spoiler like this one:
http://www.mytoyotasupramk3.com/images/mk3.jpg
I don't know if that qualifies as a spoiler (for lack of a better word) or not. As far as I know, my car is completely stock, except for replacement parts that have failed.

Okay, that is the pre-89 spoiler, so your Yellow Box should be the correct one. Well, I was hoping I could help you out with this but that's pretty much all I can think of...

You might want to use a Volt Meter and check for Voltage fluctuations out of the sending unit when someone presses on the brake. I don't know what the power is supposed to be, but if it's working there should be a change.

mines a 91 N/A and i had the yellow box. the way i understood it was that all N/A's had the yellow box and turbo's had the white box. could be wrong. its possible that whomever bought the supra new ordered an N/A with a spoiler...just a thought

I had a problem with all the electronics in the back going berserk about a month ago. Did you check your ground screws? That was my problem and all I did was tighten them.