Third light works rest of breaks light dont work

Yes, you should have power at the brake switch. If the fuse is OK. you have a bad connection or broken wire

I would check the turn signal switch first. The brake lights may go thru the switch depending on the configuration.

Usually when the third brake light works but the regular lights don't the problem is in the turn signal switch.
I would check for voltage there.

I don't know if this will solve your problem, but it might help. I had an early model Toyota Tarago, with brake lights that seemed to work when they felt like it. I cleaned out the dust around the globes in the holders, but the only thing that worked was to place a match in the holder, so that the globe was held firmly. No more problems. Obviously, if I could have afforded new holders, that would have solved it also.

Not even the third eye? then the fuse is blown or all the bulbs are out or the brake light switch on the break pedal is bad wire off or broken( it breaks right off the plug then crosses then blows the fuse as the loose broken wire hits the brake pedel arm. Test the break pedal switch first if the third eye doesesnt work either. no power with a test light the fuse is blown or the wire broke ( the wire goes straight to the switch from the fuse and doesnt go anywhere elese. the other wire if hot should light the lights. Most of these wont come out of park without this working as the wire also turns on the park release but some Fords the park release sticks released and Ford made em that way as they didnt like the brake to get out of park law. If the brake lights dont work maybe you ought not be able to get out of park anyway till its fixed. the switch is hot on both wires with the switch pused down and the lights dont still work go after the third eye first if the bulbs are bad change em before you do the rest of the work. on cars with yellow turn signals the brake lights all work on the same wire but red only use three wires, but you didnt say the turn signales didnt work if they work and they are red you r on the way to the turn signal switch as the brake switch powers the turn switch with power then it splites it fot the two lights and adifferent switch circuit for the front hooks them all together for hazard. yellow turns in the back or even separt bulbs can mean blown bulbs ther too its old enought for all the bulbs to fail and the runs still work.

Turn signal switch.

check for bloown fuse

disconect the break light switch and link a piece of wire between the two terminals and the break lights should come on

checks contacts

Most likely a short in your break line. You might also check the brake switch, but I would think if the break switch was going, it you wouldn't even have the third lite working...