> my US mazda cx5 center brake light flashes when you press the brakes.
That is not a factory feature, it's almost certainly a dealer-installed piece of junk like this (https://pulseprotects.com/product-info/) which the dealer almost certainly charged a stupid amount of money for, and as noted it's not actually legal in the US.
Around me the local Hyundai/Kia chain loves to install those, and I hate them.
As you may be aware, the US is a confederation of states. The type of light that flashes several times at the initiation of braking is specifically authorized by the California Vehicle Code, and perhaps in other states.
Do you have a reference as to where it's allowed in the CVC? FMVSS section 108 table I-c specifies this for the stop light:
Steady burning.
Must be activated upon application of the service brakes.
When optically combined with a turn signal lamp, the circuit must be such that the stop signal cannot be activated if the turn signal lamp is flashing. May also be activated by a device designed to retard the motion of the vehicle.
(a) Any motor vehicle may also be equipped with a system in which an amber light is center mounted on the rear of a vehicle to communicate a component of deceleration of the vehicle, and which light pulses in a controlled fashion at a rate which varies exponentially with a component of deceleration.
(b) Any motor vehicle may be equipped with two amber lamps on the rear of the vehicle which operate simultaneously with not more than four flashes within four seconds after the accelerator pedal is in the deceleration position and which are not lighted at any other time. The lamps shall be mounted at the same height, with one lamp located on each side of the vertical centerline of the vehicle, not higher than the bottom of the rear window, or if the vehicle has no rear window, not higher than 60 inches. The light output from each of the lamps shall not exceed 200 candlepower at any angle horizontal or above. The amber lamps may be used either separately or in combination with another lamp.
(c) Any stoplamp or supplemental stoplamp required or permitted by Section 24603 may be equipped so as to flash not more than four times within the first four seconds after actuation by application of the brakes.
> According to a document by SafeLite of America, Inc., that you enclosed, its product Safe-T-Stop "will pulse [the center high mounted brake light] for approximately 6 seconds and reactivate if the brakes are reapplied." You read S5.5.10(d) of Federal Motor Vehicle Safety Standard No. 108 as requiring "that the third brake light must be wired to be steady-burning," and that you believe that Safe-T-Stop "contravenes this requirement of the standard by varying the brightness of the light."
> We confirm your interpretation. S5.5.10(a), (b), and (c) list the motor vehicle lamps that may flash when they are operated. No stop lamp is among the lamps listed. S5.5.10(d) requires all other lamps to be wired to be steady burning, thus including all stop lamps. Standard No. 108 does not allow a stop lamp that pulses, and a vehicle with a stop lamp that pulses does not meet Federal requirements.
It's clear that there's not much enforcement, since all the dealers I've visited near me install these things by default. If you commit to a car that's not yet delivered, you can negotiate to exclude these, or you can have them remove it (but they'll most likely have cut into the factory harness to install it, so the wiring harness has been modified, which is a negative IMHO).
Personally, I find these devices to be pretty terrible. I would be fine with flashing for high intensity braking, but the flashing is attention grabbing by design, and it's inappropriate in a lot of situations as it distracts from gathering awareness of the surroundings.
No one cares, not all states have mandatory inspections, and many inspectors just check if the brake light comes on when they press the brake pedal which would not reveal such an aftermarket device.
The only way to catch something like this would be a road driving test by the inspector, and even here in Europe this is not required.
IIRC in the USA there are features allowed to be installed aftermarket that aren't legal to be installed as a dealer option (like front side-window tinting)
That is not a factory feature, it's almost certainly a dealer-installed piece of junk like this (https://pulseprotects.com/product-info/) which the dealer almost certainly charged a stupid amount of money for, and as noted it's not actually legal in the US.
Around me the local Hyundai/Kia chain loves to install those, and I hate them.