Supplemental Brake... Necessity or Preference

I've seen that publication before...and it is fairly comprehensive, but it isn't a law that was passed by the California state legislature. A judge is not bound to it. I prefer citing the law directly - however obscure it may be.

There is a 2nd post immediately below the referenced post in the smartcarofamerica.com link that refers to section 26508 (Emergency stopping). Subsection (d) reads:

d) Towed vehicles shall be deemed to be in compliance with this section when:

(1) The towed vehicle is equipped with a no-bleed-back relay-emergency valve or equivalent device, so designed that the supply reservoir used to provide air for the brakes is safeguarded against backflow of air from the reservoir through the supply line.

(2) The brakes are applied automatically and promptly upon breakaway from the towing vehicle and maintain application for at least 15 minutes, and

(3) The combination of vehicles is capable of stopping within the distance and under the conditions specified in subdivisions (k) and (l).

Section 26508 does not appear to be referenced from within another section (like 26454 is), but it is referenced in the "One Point Count California Vehicle Code Violations" table of the point violations against one's drivers license. Sometimes all of the relevant information is scattered across several sections.