Hi Falcon_Lake: We have only recent familiarity with Texas area crossings, but, they are extremely lax there. The last 2 times we have entered via Nuevo Laredo ( there was a "nothing to declare" lane (You have nothing to declare because it´s all personal use stuff). When you drive through the Customs part, they take a look at you and wave you on. No "red light/green light". When we went through in December nobody was there (Christmas Party I think)
When we went through in July the buzzer went off so we drove in to the revision and the guy said in Spanish, basically "Whatcha stoppin for?" The buzzer went off "What the buzzer went off for?" We don´t know. He then asked us to open our trunk, he look bored and told us to continue.
So, it depends on where you cross I think.