Carnal is a widely used slang term in Mexico for 'brother'. It extends beyond biological siblings to mean a very close friend, much like 'bro' or 'homie' in English.
The word originates from carne (flesh), beautifully illustrating the deep, 'flesh and blood' bond it represents. In the song, the narrator addresses his friend as carnal, highlighting the profound trust and loyalty that are central themes in this emotional corrido.
This song is a corrido, a story-song, told from a really unusual perspective: the main character is already gone. He's speaking from the afterlife. The singer tells us his name is Arturo and that death came for him unexpectedly. He says, "No alcancé a despedirme porque no pensaba / Que la muerte me esperaba" (I didn't get to say goodbye because I didn't think / That death was waiting for me). Now, he's looking back on his life and sending messages to the people he left behind.
Arturo remembers his life in Houston, Texas, especially his beloved truck, which he calls "la más chingona" (the baddest one). He regrets that he can't drive it anymore, remembering the races and the fast life. He asks his brother to look after his daughters, his "mayor tesoro" (greatest treasure), and tells his parents he'll be with them in the wind and the rain. Even though he's gone, he says he left happy, "bien alegre montado en mi ranfla" (very happy riding in my car), and wants his friends to remember him whenever they hear the roar of big truck engines.