Method and apparatus for testing electrical circuits of a recreational vehicle are disclosed. The method incorporates use of a printed circuit board assembly supporting a plurality of vehicle interface contacts; a controller programmed with vehicle diagnostics code that communicates with each vehicle interface contact. Each vehicle interface contact communicates with a corresponding circuit of the recreational vehicle. Each circuit of the recreational vehicle is operatively responsive to an execution by the controller of a corresponding portion of a vehicle diagnostics code. The method includes steps of plugging an electrical-systems utility plug of the recreational vehicle into an electrical system diagnostics device; automatically determining an operative status of a battery of a battery circuit of the recreational vehicle; and confirming that a turn signal circuit of the recreational vehicle, cooperating with the electrical system diagnostics device, operates to provide a flashing hazard warning circuit for the recreational vehicle.