Why do only one brake light work?

Check your fuses. They are usually located in the glove box. They are easy to change and only cost about $5 for a box. Check your manual to see which fuse is for the lights, if the medal bar is broken you need a new fuse.

I have a 1977 Chevy Impale,the brake light wan't work and when turn on the turn signal to right the left come on also.Do you know the problem.

check the brake light switch,on the brake pedal. it may be out of adjustment or just plain faulty.

I just recently had this fixed on my 2000 Pontiac Grand Prix. The brakes lights were out on both sides but worked in the rear glass. Ended up being the turn signal switch which for my car was a $350 part and with labor was a total of $507. Good Luck!

You may have a short in your wireing. Also your wires might not be hooked up to your lights.check your plugs and if they are good you might want to take it in to a shop.

it is common for your earth wire/s in the brake light plastic housing to have a bad connection and can be corrected by tightening the screw that fixes it to the housing.(located near where the bulb/s fit)

On my LHS, it appears that the switch that connects to the brake pedal went out. Hence, all of the brake lights do not work. Something to check out as well in doing your diagnostics.