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From Sections 25250-25282 California Vehicle Code, Division 12, Chapter 2, Article 7
(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
It appears a flashing brake light is legal within the stated limits.
This is an example of what a former co-worker of mine, who is also a preacher, calls "prooftexting", wherein a small section of a book is taken out of context in order to attempt to prove something. While perhaps no real malice is intended by people who will go to the lawbooks to try to find a real answer, the danger is that they will often miss context (either deliberately or accidentally) and pass out very bad advice, which can get people ticketed or their cars towed, or both. Maybe you've already been "prooftexted to" on another forum, or whether you dug this up on your own, it's important to note that what the snipped of law you provided seems to say, and what it really says, are quite different.
If you're going to cite a state law, even part of one, you'd do well to cite the law properly, or at the very least say what state
it's from. It wasn't difficult at all to find that it is California State Vehicle Code, but it's still better to cite it properly.
You should also take note that the partially quoted Vehicle Code Division 12, Chapter 2, Article 7, 25251.5. (a) code refers to Section 24603, which is in Article 3 of the aforementioned Division and Article. That's a large omission, because that section states, inter alia
(h) Any supplemental stoplamp installed after January 1, 1987, shall comply with Federal Motor Vehicle Safety Standard No. 108 (49
C.F.R. 571.108). Any vehicle equipped with a stoplamp that complies with the federal motor vehicle safety standards applicable to that
make and model vehicle shall conform to that applicable safety standard unless modified to comply with the federal motor vehicle
safety standard designated in this subdivision.
Another quote from paragraph (e)
All stoplamps shall be plainly visible and understandable from a distance of 300 feet to the rear both during normal sunlight and at
A flashing/pulsing/throbbing/swirling/gyrating stop lamp might be plainly visible from such distances, but it more certainly is not going to be plainly *understandable*.
But this is all academic, because FMVSS 108 is the governing law in California and in any other State of the Union. Their own law references FMVSS 108, but even without that explicit declaration, 49 CFR 571.108 is the higher authority.
In short: No, flashing stop lamps, including CHMSLs, are not legal.