My '94 GT's rear tail lights don't turn on

didn't you just try to paint them? make sure you have them plugged in right. make sure you have all the bulbs in right. make sure none of them blew out with you messing with the lights. basically go over everything you touched.

Also make sure they have a good ground.

Did you put 3156 bulbs in, instead of 3157's?

The ground shouldn't be an issue, since both the low and high share the same ground wire. If the high is working, then the low also has ground.

Are you getting 12V at the bulb socket (labeled MINOR) when the taillights (running lights) are on?

Rick