Taco de Carlos was an experimental spinoff of the Carls Jr. chain in the 1970's and early 1980's that featured, what else? Mexican food. My family went several times to the one that was at Brookhurst and Warner in Fountain Valley (right next to a standard Carls Jr. that is still in business). I don't remember anything about the food but I remember being very intrigued by the kitschy Happy Star character sporting a sombrero.
Does anyone else remember Taco de Carlos?