reverse/taillight fuse under driver side left fusebox panel
They are tied to either the brake lights or the tail lights.
Look for a fuse labeled TAIL LIGHTS. There are 2 separate circuits, one for brake turn and flasher and the other is for tail lights.
should be the tail lights fuse
Fuse
Tail lights and brake lights fuse.
replace fuse
Probably a blown fuse.
Tail lights are usually on the same fuse with interior lights and dash lights. That is so you will know when the fuse is blown. Brake lights are usually on a different circuit. If a fuse is blown, try to figure out the cause rather than just replacing the fuse.
It could be a blown fuse. Tail lights and brake/turn are on separate fuses. Apparently there is not a ground problem since brake/turn works OK.
Are you saying your tail lights themselves do not work and only the brake lights work. If that is the case, check the fuse, and then check the tail light bulbs.
for the tail lights all the other lights are working blanking lights brake lights and reverse lights but no tail lights on both side
The GMC dash tail and parking lights are on a different fuse from the brake lights. Check the fuses for a possible blown fuse.