Unable to find out why the upper brake light work but the lower two by the tail lights don't on a chevy venture 2004 the bulbs look good and the fuse isn't back and have been replace, what else good it be besides a short in a wire?

Tony, our TB's only have 3 bulbs, 1 brake, 1 running, 1 backup.
If you happened to be playing with NEW LED bulbs (from local retail location) for the brakes, guaranteed you blew the fuse under the rear seat. It takes a special CK socket for the brakes that no one carry's. If you're only dealing with normal incondecent bulbs, I'd still check the fuse under the rear passenger seat.

The tail light assembly on this vehicle is a poor fit and moisture softer invades the bulb assembly when it rains. Remove the tail light assembly and replace any bulbs that have shorted out. You may need to replace the assembly.

check the light checking unit power for light go through this to the bulbs tell you when a bulb is out. center light is not on this circuit.

feed supply problem somewhere ?but where ? try checking the wiring loom at the rear or as its called in american "pigs tails"

tail lights and brake light use a different eliment in the same bulb

you don`t say if its both or just one brake light out.you say the light itself is on but not if you mean tail light or what.the tail lights use a different filament in the bulb than the signal light which is the same filament that the brake light uses.if the signal light work on the rear then the bulbs are good,if just one side works then the bulb is no good on the side that doesn`t work.if the signal lights work but neither brake light works then you need to check the fuses in the fuse panel under the dash on the drivers side.if the fuses are good then it will be either a bad wire at the brake switch or a bad brake light switch,this is located on the brake pedal lever under the dash.

it could be a bad ground in the tail lights

I would start by trying another bulb. Even though the brake and tail light share the same bulb they actually are powering different filaments inside of the bulb so you can have a tail light filament that is working fine and illuminating properly but have a burned out brake light element that won't work at all...all inside the same bulb. Not uncommon at all to see this problem and these bulbs are pretty inexpensive.

I had this same problem i cleaned contacts that the bulb goes in and put dialectic greese on them.Also one bulb I think on passenger side brake light.one element shorted.Replace bulb and you should be all set.Dont ask me why.Must be bad design.

My van did the same thing it was the ground at the socket it had a good ground all the way to the socket but lost it right at the socket.