What is the test for reasonable cause for a search of a vehicle following a stop by a police officer?

In Bramlette v. Superior Court (1969) 273 Cal.App.2d 799, 78 Cal.Rptr. 532, it was held that where an officer properly stopped a panel truck for investigation, discovered the occupants were minors, and observed an opened partly empty jug of wine in the vehicle which was accessible to all of the occupants, he could reasonably assume that the offense of possession of an intoxicating liquor by a minor in violation of section 25662 of the Business and Professions Code was being committed in his presence. The arrest of the minors (see Pen.Code, 836, subd. 3) was upheld. The prosecution was permitted to use the fruits of a subsequent search of the vehicle which revealed marijuana seeds in plain sight, and other marijuana and paraphernalia discovered in the framework and other parts of the vehicle, [14 Cal.App.3d 944] and contraband which was apparently discarded by the accused while they were being transported in the patrol car (273 Cal.App.2d at p. 806, 78 Cal.Rptr. 532).

In People v. Cowman (1963) 223 Cal.App.2d 109, 35 Cal.Rptr. 528, it was found that the officers had reasonable cause to stop the defendants' vehicle for investigation. The court noted, '* * * when the officers approached the car, after it had stopped, they observed the occupant in the rear seat drinking out of a beer bottle. It would seem that this observation would have been sufficient to justify the arrest of the driver of the vehicle and the party drinking the beer as well as a search of the vehicle. (Veh.Code, 23121, 23122 and 23123.)' (223 Cal.App.2d at p. 118, 35 Cal.Rptr. at p. 534.) (The search was in fact justified by the defendant's subsequent consent.)