I have a 1983 Chevy silverado and I changed two of the relays for the lights and was wondering if there was still another fuse because they still don't work, yet the brake lights and signal lights work.?

SOURCE: Tail lights don't work on 1998 Chevy Silverado.

check the wiring from the tailights back to the fuse panel, it sounds like an open connection. if i recall correctly check under the dash on the drivers side near the fuse panel for a bunch of wires in a bundle and look carefully for a wire or two that are cut/shorted/or seperated, you can also check under the drivers side kick panel by the hood release.

SOURCE: Brake lights on my Chevy Silverado do not work but the Cab works

check grounds on rear light assy's

SOURCE: No tail lights on 1991 Chevy Silverado. fuse is good

sounds like a broken wire in the harness. look around the bumper area,sometimes along the frame. may have to peel back some tape covering. also if you have a trailer harness look closely at those.

SOURCE: 2004 chevy 1500 brake lights not working

check fuse under hood, batery terminals coroded wire at harness if everything fails run a hot wire to rear brake line with an interuptor.
check the swich under the foot brake.
vitally

SOURCE: 99 Chevy Tahoe... Rear turn signals, brake lights, and hazards

I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!