Why are tail lights staying on constantly?

the 65 has the sequential taillights and if you have the original module it may be shorted out. The unit is in the trunk by the back seat. Check it first. If it is bad, you may be able to find an original but there are third party solid state units today that eliminate this problem.

"Short to power" somewhere in the tail-light circuit, Start at the tail-lights in the rear and if you can trace the wires back to the fuse or relay looking for burnt or open spots along the wire.

Sorry, if they were shorted, they would not work at all and blow a fuse. It is more than likely in the flasher assy.

If it was in the flasher assy then wouldn't the tail-lights flash with the turn signals? And i mean short the power not short to ground, like feedback from another power source along the wire somewhere. But you could just as well be right so i would check that too.

I don't know if you have ever seen an original 65 Bird flasher unit but it is NOT solid state and is actually a good piece of electronic engineering. It is possible that the flasher circuit could have an open circuit and not flash but just keep the lights on.

if the brake lights are on and only the brake lights not running lights check the brake pedal the switch underneath it is staying on you have to adjust it back it off a little until it goes off and comes on when the brake pedal is applyed.and off when it is let off.

I have a 66 ford school bus hooked battey up tail lights stay on looked the dash cant see a brake switch any where