1988 Chevy Truck tail lights don't work

i recently reran an antenna cable through my dash. afterwords my tail lights quit. i've checked them with a tester & i have power all the way to the bulbs(which are good), but no lights. i'm thinking there is a ground problem. is there a ground wire for the rear tail lights under the dash? my license plate lights work. i have a shell with a 3rd brake light spliced into the drivers side tail light harness, both the ground wire & hot wire light the tester, it has to be a ground problem, but where? i have to have disturbed it under the dash somewhere, any clues as to where it could be? thanks in advance