There are a few states that restrict the use of amber brake lights to vehicles made on or after January 1, 1979.
That doesn't sound right. There are states that restrict the use of amber stop lamps to vehicles made
before a certain date, though. The relevant SAE standard permitted stop lamps to be red or yellow ("amber") until 1970, but in practice amber stop lamps were almost never installed on vehicles. There were a few British cars with them in the 1950s and early '60s, and maybe one or two others, but by the time FMVSS 108 took effect in 1968 with red as the only acceptable color, red had been the only color in use for years.
The Federal preemption provision says any state vehicle equipment regulation must be identical to the Federal regulation dealing with the same kind of vehicle equipment, and that any aspect of a state regulation that is
not identical to the Federal regulation is null and void. In theory, this runs both directions; it says "identical" so a state can't have a standard that has tighter, looser, or different technical requirements vs. the Federal standard. In practice, though, at the practical level it means states can't have a standard that is tighter or different, because enforcing state standards is left to the states. Many states' vehicle equipment codes are quite a lot looser than the Federal standard. Some states still have old language on the books allowing yellow stop lights, but it would be foolish to modify a car's stop lights to make them amber. Not only does it greatly increase the chances of being badly hit in traffic (because of the nonstandard signal) but it also means high likelihood of getting a ticket, definitely in another state, but quite possibly even in-state from an officer who might well write the ticket despite the provision allowing yellow stop lights.
What definitely can't be enforced is state standards that are tighter than the Federal standard. A state couldn't require yellow rear turn signals, because the Federal standard allows red or yellow. A state couldn't require turn signal repeaters, because the Federal standard doesn't require them. Old state standards limiting headlight bulbs to 32 candlepower, etc, are not enforceable; they would make every vehicle on the road noncompliant.
But I'm not completely sure how we got distracted by amber stop lights. Robertkoa, if you were to use LED bulbs (which you should be careful about, because there's not yet such a bulb that works effectively, legally, and safely in every/any lamp, see
here and
here. If you do wind up trying LED bulbs, the correct strategy is red LEDs behind red lenses.
