Roid Warrior, from what I'm remembering from my academy training way back in 97, the Terry Frisk can extend to a vehicle, based on the same circumstance as the Terry Frisk for a person. It's all about articulating why you felt the need to do it, i.e., furtive movement and so on.
This is what I found to reference it, although I'm too tired to do a more detailed search: 3. Car Frisk - A so-called "car frisk" (protective search of interior of vehicle to locate weapon) may be conducted where an officer has reasonable suspicion that a person is dangerous and a weapon may be in the vehicle that could be used to harm him. This search may be no more intrusive than is necessary to locate a weapon. The legal standards for the car frisk are essentially the same as for the frisk of a person. Remember that under the recent U.S. Supreme Court case, Maryland v. Wilson, 117 S.Ct. 882 (1997), officers have the authority to order passengers of a stopped vehicle to exit the car. This option can be expected to make car frisks--as well as the frisks of the occupants themselves--safer and more effective. [Please note the Wilson case does not give officers the authority to automatically frisk occupants, but merely the authority to ask them to step from the car.]
The bottom line is, do the police perform illegal searches? Yes, they do, and believe it or not, many of them are not taught correctly what is illegal and what isn't, and some when they find it choose to ignore it. I had a video camera in my patrol car, and because I believed in doing things right, I chose to follow what I could and could not do legally. You can make a fool outta a police officer should he write that he felt what he believed to be a weapon in your pocket , let's say a knife, and then finds narcotics on you as I know damn well, a baggie of narcotics feels nothing like a knife and a good defense attorney can show this in court. It all depends on where you are. Many officers carry tape recorders and more and more units have video equipment in them. The best thing to do is to be aware of what they can or cannot do. Unfortunately, the old statement, "you can beat the rap, but you can't beat the ride" is alive and well.