Noticed today that both brake lights work, but when I turn on the right signal, the left brake light goes out. I have changed bulbs and no difference.

Help me please!!!!!!!!!!!!!

Do your park lights work ok? Your brake lights and the turn signal lights use the same part of the bulb, so if the brake lights work...changing the bulb will be of no help. I would start suspecting the turn signal switch in the column, esp since you state your brake lights are working ok. Just a quick check, are your front signals doing the same as the back? you may have a front bulb out.

All of the lights are working. It is really weird that it only happens when I turn on the right turn signal.

Check the grounds to the rear sockets. If they are OK you have a bad switch. What year are we working with. Some of the mid 60,s you can take the horseshoe off the switch & bend the contacts a little to fix it.

its a 72

The 68 up all had a plastic switch that is sealed. Often the horseshoe breaks in the center where the lever atataches. You can often fix it with superglue. You should be able to feel it go into an on position. Again check your grounds & run a ground wire between the bed & frame.

grounds are fine... 99.9% chance in that. If the bulb lights up, then there is a ground. If it keeps on turning off when the signal is turned on, but acts normal the rest of the teim... then you are probably looking at a turn signal switch.

do yall mean inside the steering column? if so, is there some instructions?

brake lights run through the turn signal switch, I would guess you most likely have a bad turn signal switch, I see this alot, a good check , not always conclusive, but might help you, start up the truck (so your battery dont die)let it idle and have someone sit in the drivers seat with his/her foot on the brake, while you are in the back looking at the brake lights,(I am gonna assume they are both on right now) have him/her flip on the turn signal to the right, or whichever direction it kills the other brake light, while the brake light is out and the turn signal is on, have her / him bounce the turn signal lever without taking it out of its position while you are watching the brake lights, does the one that was out ever flicker or come on at all, this will prove to you that the signal switch is most likely going to be your issues.
You may have to buy the adapter when replacing the switch, good luck and keep us informed

it wqas the switch and my dad replaced it for me.

thanks a lot guys!